We already trap a bunch of existing features for the purpose of
disabling them (MAIR2, POR, ACCDATA, SME...).

Let's move them over to our brand new FGU infrastructure.
Reviewed-by: Joey Gouly <joey.gouly@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20240214131827.2856277-20-maz@kernel.orgSigned-off-by: Oliver Upton <oliver.upton@linux.dev>