vdpa/mlx5: Propagate link status from device to vdpa driver

vdpa/mlx5: Propagate link status from device to vdpa driver

Add code to register to hardware asynchronous events. Use this
mechanism to track link status events coming from the device and update
the config struct.

After doing link status change, call the vdpa callback to notify of the
link status change.

Signed-off-by: Eli Cohen <elic@nvidia.com>
Link: https://lore.kernel.org/r/20210909123635.30884-4-elic@nvidia.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>