lava: Fix bundle to use for RPi64
AUM tests fails on RPi 4b boards due to incorrect OSTree and bundle expectation.
arm64-rpi64 bundles don't exist.
RPi64 boards use arm64-uboot bundles for the upgrade.
https://phabricator.apertis.org/T8487
Signed-off-by: Frédéric Danis frederic.danis@collabora.com