Backports v2023dev1 → v2022

Add systemd service to delay boot

Rollback tests need to reset the DUT before boot is completed.
This commit add a service delaying start of AUM and user logging, and
displaying a message allowing a tester to reset the board.
This service should be run before systemd-bless-boot.service which rename
the EFI loader entry discarding the bootcount.

Fix OSTree branch used for RPi64

OSTree branch installed on RPi 4b boards use
`origin:apertis/v2023dev1/arm64-rpi64/fixedfunction` instead of
`origin:apertis/v2023dev1/arm64-uboot/fixedfunction` . The later is generic
for R-Car and RPi 4b boards.

This commit adds a function to return the expected branch, and adapt it
for the RPi64.

https://phabricator.apertis.org/T8487

Signed-off-by: Frédéric Danis frederic.danis@collabora.com