KVM: arm64: selftests: Add some tests for GICv2 in vgic_init

Add some GICv2 tests: general KVM device tests and DIST/CPUIF overlap
tests.  Do this by making test_vcpus_then_vgic and test_vgic_then_vcpus
in vgic_init GIC version agnostic.

Signed-off-by: Ricardo Koller <ricarkol@google.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20211005011921.437353-9-ricarkol@google.com