media: Documentation: media: Refer to mbus format documentation from CSI-2 docs

The media bus formats to be used on serial busses are documented but there
was no reference from CSI-2 documentation. Add that now.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Acked-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Documentation/driver-api/media/csi2.rst

@@ -8,6 +8,12 @@ the host SoC. It is defined by the `MIPI alliance`_.
 
 .. _`MIPI alliance`: http://www.mipi.org/
 
+Media bus formats
+-----------------
+
+See :ref:`v4l2-mbus-pixelcode` for details on which media bus formats should
+be used for CSI-2 interfaces.
+
 Transmitter drivers
 -------------------