KVM: arm64: Make ID_REG_LIMIT_FIELD_ENUM() more widely available

ID_REG_LIMIT_FIELD_ENUM() is a useful macro to limit the idreg
features exposed to guest and userspace, and the NV code can
make use of it.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Joey Gouly <joey.gouly@arm.com>
Link: https://lore.kernel.org/r/20250220134907.554085-8-maz@kernel.org


Signed-off-by: Oliver Upton <oliver.upton@linux.dev>