KVM: arm64: vgic: Allow registration of a non-maskable maintenance interrupt

KVM: arm64: vgic: Allow registration of a non-maskable maintenance interrupt

Our Apple M1/M2 friends do have a per-CPU maintenance interrupt,
but no mask to make use of it in the standard Linux framework.

Given that KVM directly drives the *source* of the interrupt and
leaves the GIC interrupt always enabled, there is no harm in tolerating
such a setup. It will become useful once we enable NV on M2 HW.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230103095022.3230946-3-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>