Seeing source was changed in 2012, I also believe it's long dead; for reference, here's the list of targeted platforms:
# config                package                 build           install
# target                name                    target          target(s)
#
efikamx                 efikamx                 u-boot.imx      u-boot.imx
highbank                highbank                -               u-boot.bin
igep0020                igep0020                -               u-boot.bin
mx51evk                 mx51evk                 u-boot.imx      u-boot.imx
mx53ard                 mx53ard                 u-boot.imx      u-boot.imx
mx53loco                mx53loco                u-boot.imx      u-boot.imx
mx6qarm2                mx6qarm2                u-boot.imx      u-boot.imx
mx6qsabrelite           mx6qsabrelite           u-boot.imx      u-boot.imx
omap3_overo             omap3-overo             -               MLO u-boot.img u-boot.bin
omap3_beagle            omap3-beagle            -               MLO u-boot.img u-boot.bin
omap4_panda             omap4-panda             -               MLO u-boot.img u-boot.bin
omap4_panda_splusb      omap4-panda-splusb      -               MLO u-boot.img u-boot.bin spl/u-boot-spl.bin
omap4_sdp4430           omap4-sdp4430           -               MLO u-boot.img u-boot.bin
origen                  origen                  -               u-boot.bin spl/origen-spl.bin
smdk5250                smdk5250                -               u-boot.bin spl/smdk5250-spl.bin
snowball                snowball                -               u-boot.bin
vexpress_ca9x4          ca9x4-ct-vxp            -               u-boot.bin
vexpress_ca9x4          vexpress-ca9x4          -               u-boot.bin
vexpress_ca5x2          vexpress-ca5x2          -               u-boot.bin

And this is the one from the u-boot package:
# ARCH  subarch         platform        target
# --------------------------------------------
armel   -               dockstar        u-boot.kwb
armel   -               dreamplug       u-boot.kwb
armel   -               guruplug        u-boot.kwb
armel  -               openrd_base u-boot.kwb
armel  -               openrd_client u-boot.kwb
armel  -               openrd_ultimate u-boot.kwb
armel   rpi             rpi             u-boot.bin
armel   -               sheevaplug      u-boot.kwb
armhf   exynos          arndale         u-boot-dtb.bin spl/arndale-spl.bin
armhf   exynos          odroid          u-boot-dtb.bin
armhf   exynos          odroid-xu3      u-boot-dtb.bin
armhf   imx             mx53loco        u-boot.imx
armhf   imx             mx6cuboxi       u-boot.img spl/u-boot-spl.bin SPL
armhf   imx             nitrogen6q      u-boot.imx
armhf   imx             novena          u-boot.img spl/u-boot-spl.bin SPL
armhf   imx             udoo            u-boot.img spl/u-boot-spl.bin SPL
armhf   imx             usbarmory       u-boot.imx
armhf   imx             wandboard       u-boot.img spl/u-boot-spl.bin SPL
armhf   tegra           jetson-tk1      u-boot-dtb-tegra.bin
armhf   omap            am335x_boneblack u-boot.img spl/u-boot-spl.bin MLO
armhf   omap            am57xx_evm      u-boot-dtb.img spl/u-boot-spl.bin MLO
armhf   omap            dra74_evm       u-boot.img spl/u-boot-spl.bin MLO
armhf   omap            igep0020        u-boot.img spl/u-boot-spl.bin MLO
armhf   omap            nokia_rx51      u-boot.bin
armhf   omap            omap3_beagle    u-boot.img spl/u-boot-spl.bin MLO
armhf   omap            omap4_panda     u-boot.img spl/u-boot-spl.bin MLO
armhf   rockchip        firefly-rk3288          u-boot-dtb.img spl/u-boot-spl-dtb.bin
armhf   rpi             rpi_2           u-boot.bin
armhf   sunxi           A10-OLinuXino-Lime      u-boot-sunxi-with-spl.bin
armhf   sunxi           A10s-OLinuXino-M        u-boot-sunxi-with-spl.bin
armhf   sunxi           A20-Olimex-SOM-EVB      u-boot-sunxi-with-spl.bin
armhf   sunxi           A20-OLinuXino-Lime      u-boot-sunxi-with-spl.bin
armhf   sunxi           A20-OLinuXino-Lime2     u-boot-sunxi-with-spl.bin
armhf  sunxi            A20-OLinuXino_MICRO     u-boot-sunxi-with-spl.bin
armhf   sunxi           Bananapi        u-boot-sunxi-with-spl.bin
armhf   sunxi           Bananapro       u-boot-sunxi-with-spl.bin
armhf   sunxi           Cubieboard      u-boot-sunxi-with-spl.bin
armhf   sunxi           Cubieboard2     u-boot-sunxi-with-spl.bin
armhf   sunxi           Cubietruck      u-boot-sunxi-with-spl.bin
armhf   sunxi           Lamobo_R1       u-boot-sunxi-with-spl.bin
armhf   sunxi           Linksprite_pcDuino      u-boot-sunxi-with-spl.bin
armhf   sunxi           Linksprite_pcDuino3     u-boot-sunxi-with-spl.bin
armhf   sunxi           Mini-X  u-boot-sunxi-with-spl.bin
armhf   sunxi           orangepi_plus   u-boot-sunxi-with-spl.bin
arm64   tegra           p2371-2180      u-boot-dtb.bin
avr32   -               hammerhead      u-boot.img
mips    -               qemu_mips       u-boot.bin
sh4     -               r2dplus         u-boot.bin
sh4     -               sh7785lcr_32bit u-boot.bin

Some of the dropped platforms might still be in use here and there, e.g. vexpress or highbank might be used for QEMU or in our own DC, but I doubt these systems need bootstrapping from 17.10.