arm64: Add capability denoting FEAT_RASv1p1

arm64: Add capability denoting FEAT_RASv1p1

Detecting FEAT_RASv1p1 is rather complicated, as there are two
ways for the architecture to advertise the same thing (always a
delight...).

Add a capability that will advertise this in a synthetic way to
the rest of the kernel.

Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Link: https://lore.kernel.org/r/20250817202158.395078-2-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>