media: uvcvideo: Implement mask for V4L2_CTRL_TYPE_MENU

Replace the count with a mask field that lets us choose not only the max
value, but also the minimum value and what values are valid in between.

Suggested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>