This commit move IRQ request and free operations from probe()
to VIRTIO status change handler to comply with VIRTIO spec.

VIRTIO spec 1.1, section 2.1.2 Device Requirements: Device Status Field
The device MUST NOT consume buffers or send any used buffer
notifications to the driver before DRIVER_OK.
Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
Link: https://lore.kernel.org/r/1589270444-3669-1-git-send-email-lingshan.zhu@intel.comSigned-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>