ifcvf: move IRQ request/free to status change handlers

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.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>