media: docs: Deprecate mfc frame skip control

Deprecate mfc private frame skip mode control for new
clients and use the standard one instead.
Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>
Reviewed-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst

@@ -2842,6 +2842,11 @@ MFC 5.1 Control IDs
 ``V4L2_CID_MPEG_MFC51_VIDEO_FRAME_SKIP_MODE``
     (enum)
 
+    .. note::
+
+       This control is deprecated. Use the standard
+       ``V4L2_CID_MPEG_VIDEO_FRAME_SKIP_MODE`` control instead.
+
 enum v4l2_mpeg_mfc51_video_frame_skip_mode -
     Indicates in what conditions the encoder should skip frames. If
     encoding a frame would cause the encoded stream to be larger then a