KVM: arm64: Add a predicate for testing if SMCCC filter is configured

Eventually we can drop the VM flag, move around the existing
implementation for now.

Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20231004234947.207507-2-oliver.upton@linux.dev


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