[backport v2022 <- v2023pre] lava/devices: rpi64: Use altbootcmd when needed

When running the aum-rollback-blacklist test, u-boot must rollback to the older version when the bootlimit of 3 has been reached.

Using just boot will bypass the boot count check, so we need to add the check here in the device template, like it is done for the other device types.

This is a backport of !481 (merged)

https://phabricator.apertis.org/T9097