[media] uvcvideo: Embed uvc_control_info inside struct uvc_control

Now that control information structures are not shared between control
instances, embed a uvc_control_info instance inside the uvc_control
structure instead of storing a pointer.

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