[media] uvcvideo: Register a v4l2_device

As a first step to the media controller integration register a
v4l2_device for each UVC control interface and make the video_device a
child of the v4l2_device.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>