refactor(amu): convert FEAT_AMUv1 to new scheme

For the FGT context save/restore operation, we need to look at the AMUv1
feature, so migrate this one over to the new scheme.
This uses the generic check function in feat_detect.c, and splits the
feature check into two functions, as was done before for FEAT_FGT.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Change-Id: I95ad797f15001b2c9d1800c9d4af33fba79e136f
2 files changed