KVM: arm/arm64: prepare GICv2 emulation to be handled by kvm_io_bus

Using the framework provided by the recent vgic.c changes we register
a kvm_io_bus device when initializing the virtual GICv2.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

include/kvm/arm_vgic.h

@@ -251,6 +251,7 @@ struct vgic_dist {
 	unsigned long		*irq_active_on_cpu;
 
 	struct vgic_vm_ops	vm_ops;
+	struct vgic_io_device	dist_iodev;
 };
 
 struct vgic_v2_cpu_if {