[media] uvc: Depend on VIDEO_V4L2

The uvcvideo driver lost its dependency on VIDEO_V4L2 during the big
media directory reorganization. Add it back.

Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>