Comment 0 for bug 1936370

[Impact]

 * u-boot-sifive package currently does not upgrade bootloader on loader1/loader2 partitions.

 * there have now been bugs identified, meaning that upgrading u-boot is required to upgrade from v5.8 kernel to v5.11 (i.e. either in-focal, or from focal to hirsute).

 * Add maintainer script that identifies if the machine one is running on is unleashed or unamtched, and appropriately upgrades the bootloader on loader1/loader2 partitions.

[Test Plan]

 * Boot older unleashed or unmatched image

 * Upgrade u-boot-sifive to latest package

 * Reboot, and observe on the serial console that u-boot version number is incremented to the latest one.

 * Repeat the test twice, once with unleashed board, once with unmatched board

 * Upgrade the package under qemu VM and observe no side-effects / no attempts to upgrade anything.

[Where problems could occur]

 * It is not possible to atomically upgrade loader1 and loader2 simultaniously.
 * A backup of loader1 and loader2 partitions is not stored anywhere.
 * Thus in case of errors rollback of older u-boot is not performed.
 * However if dd of one or the other partition fails, it is unlikely that one can restore the backup.