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.
State is Draft because u-boot does not support bootcount properly (See infrastructure/apertis-issues#130 (closed))
Fixes: infrastructure/apertis-issues#129 (closed)
Edited by Detlev Casanova