arm64: overlays don't get applied

[Paolo Pisati]

Impact:

Overlay files are dtb fragments that, upon boot, patch the main dtb board
file to enable Raspberry Pi hardware extension (commonly known as
Raspberry HATs) to work.

This mechanism works fine for the bionic/raspi2 kernel, but it didn't
work for the raspi2 arm64 variant since our dtb files are missing symbols
there.

This patch instruct the device tree compiler to add symbols to the dtb
files during the 'make dtbs' target, and fix the overlay patching
mechanism for bionic/raspi2 arm64.

The resulting increase in size is negligible (~30kb for the whole kernel
package).

Fix:

Apply the patch, build, install and reboot:

/boot/firmware/config.txt:
...
dtoverlay=pitft35-resistive

/boot/firmware/cmdline.txt:
dwc_otg.lpm_enable=0 console=serial0,115200 console=tty1 root=/dev/mmcblk0p2 rootfstype=ext4 elevator=deadline rootwait fbcon=map:10 fbcon=font:VGA8x8

dmesg:
...
[ 5.157547] fb_hx8357d: module is from the staging directory, the quality is unknown, you have been warned.
[ 5.158349] fbtft_of_value: buswidth = 8
[ 5.158362] fbtft_of_value: debug = 0
[ 5.158366] fbtft_of_value: rotate = 90
[ 5.158372] fbtft_of_value: fps = 25

ubuntu@raspi64:~$ ls -la /dev/fb1
crw-rw---- 1 root video 29, 1 Jan 28 15:58 /dev/fb1

Regression risk:

We only change how the arm64 raspi2 dtbs are generated, and since we didn't produce any image using this kernel so far, the regression risk is zero.

---

[Launchpad Janitor (janitor)]

This bug was fixed in the package linux-raspi2 - 4.15.0-1021.23

---------------
linux-raspi2 (4.15.0-1021.23) bionic; urgency=medium

  * linux-raspi2: 4.15.0-1021.23 -proposed tracker (LP: #1787151)

  * Bionic update: upstream stable patchset 2018-06-26 (LP: #1778759)
    - [Config] raspi2: CONFIG_ARM64_ERRATUM_1024718=y

  * arm64: overlays don't get applied (LP: #1782121)
    - SAUCE: arm64: dtbs: Add symbols when compiling dtb

  [ Ubuntu: 4.15.0-33.36 ]

  * linux: 4.15.0-33.36 -proposed tracker (LP: #1787149)
  * RTNL assertion failure on ipvlan (LP: #1776927)
    - ipvlan: drop ipv6 dependency
    - ipvlan: use per device spinlock to protect addrs list updates
    - SAUCE: fix warning from "ipvlan: drop ipv6 dependency"
  * ubuntu_bpf_jit test failed on Bionic s390x systems (LP: #1753941)
    - test_bpf: flag tests that cannot be jited on s390
  * HDMI/DP audio can't work on the laptop of Dell Latitude 5495 (LP: #1782689)
    - drm/nouveau: fix nouveau_dsm_get_client_id()'s return type
    - drm/radeon: fix radeon_atpx_get_client_id()'s return type
    - drm/amdgpu: fix amdgpu_atpx_get_client_id()'s return type
    - platform/x86: apple-gmux: fix gmux_get_client_id()'s return type
    - ALSA: hda: use PCI_BASE_CLASS_DISPLAY to replace PCI_CLASS_DISPLAY_VGA
    - vga_switcheroo: set audio client id according to bound GPU id
  * locking sockets broken due to missing AppArmor socket mediation patches
    (LP: #1780227)
    - UBUNTU SAUCE: apparmor: fix apparmor mediating locking non-fs, unix sockets
  * Update2 for ocxl driver (LP: #1781436)
    - ocxl: Fix page fault handler in case of fault on dying process
  * netns: unable to follow an interface that moves to another netns
    (LP: #1774225)
    - net: core: Expose number of link up/down transitions
    - dev: always advertise the new nsid when the netns iface changes
    - dev: advertise the new ifindex when the netns iface changes
  * [Bionic] Disk IO hangs when using BFQ as io scheduler (LP: #1780066)
    - block, bfq: fix occurrences of request finish method's old name
    - block, bfq: remove batches of confusing ifdefs
    - block, bfq: add requeue-request hook
  * HP ProBook 455 G5 needs mute-led-gpio fixup (LP: #1781763)
    - ALSA: hda: add mute led support for HP ProBook 455 G5
  * [Bionic] bug fixes to improve stability of the ThunderX2 i2c driver
    (LP: #1781476)
    - i2c: xlp9xx: Fix issue seen when updating receive length
    - i2c: xlp9xx: Make sure the transfer size is not more than
      I2C_SMBUS_BLOCK_SIZE
  * x86/kvm: fix LAPIC timer drift when guest uses periodic mode (LP: #1778486)
    - x86/kvm: fix LAPIC timer drift when guest uses periodic mode
  * Please include ax88179_178a and r8152 modules in d-i udeb (LP: #1771823)
    - [Config:] d-i: Add ax88179_178a and r8152 to nic-modules
  * Nvidia fails after switching its mode (LP: #1778658)
    - PCI: Restore config space on runtime resume despite being unbound
  * Kernel error "task zfs:pid blocked for more than 120 seconds" (LP: #1781364)
    - SAUCE: (noup) zfs to 0.7.5-1ubuntu16.3
  * CVE-2018-12232
    - PATCH 1/1] socket: close race condition between sock_close() and
      sockfs_setattr()
  * CVE-2018...