KVM: arm64: selftests: Make vgic_init/vm_gic_create version agnostic

Make vm_gic_create GIC version agnostic in the vgic_init test. Also
add a nr_vcpus arg into it instead of defaulting to NR_VCPUS.

No functional change.

Reviewed-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Ricardo Koller <ricarkol@google.com>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20211005011921.437353-8-ricarkol@google.com