hw/intc/arm_gic: Initialize the vgic in the realize function

hw/intc/arm_gic: Initialize the vgic in the realize function

This patch forces vgic initialization in the vgic realize function.
It uses a new group/attribute that allows such operation:
KVM_DEV_ARM_VGIC_GRP_CTRL/KVM_DEV_ARM_VGIC_CTRL_INIT

This earlier initialization allows, for example, to setup VFIO
signaling and irqfd after vgic initialization, on a reset notifier.

Signed-off-by: Eric Auger <[email protected]>
Message-id: 1426094226[email protected]
Signed-off-by: Peter Maydell <[email protected]>