arm64: Factor out checking of a feature against the override into a macro

arm64: Factor out checking of a feature against the override into a macro

Checking for a feature being supported from assembly code is
a bit tedious if we need to factor in the idreg override.

Since we already have such code written for forcing nVHE, move
the whole thing into a macro. This heavily relies on the override
structure being called foo_override for foo_el1.

No functional change.

Reviewed-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220630160500.1536744-5-maz@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>