media: uvcvideo: Refactor uvc_ctrl_mappings_uvcXX

Convert the array of structs into an array of pointers, that way the
mappings can be reused.

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>