vfio: Make vfio-pci device migration capable

vfio: Make vfio-pci device migration capable

If the device is not a failover primary device, call
vfio_migration_probe() and vfio_migration_finalize() to enable
migration support for those devices that support it respectively to
tear it down again.
Removed migration blocker from VFIO PCI device specific structure and use
migration blocker from generic structure of  VFIO device.

Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
Reviewed-by: Neo Jia <cjia@nvidia.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>