arm64/sysreg: Convert *_EL12 accessors to Mapping

Perform a bulk convert of the remaining EL12 accessors to use the
Mapping qualifier, which makes things a bit clearer.

Reviewed-by: Mark Brown <broonie@kernel.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20241219173351.1123087-4-maz@kernel.org


Signed-off-by: Will Deacon <will@kernel.org>