media: dvb rst: identify the documentation gap at the API

Now that DVB spec is almost in sync, document what's missing.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

Documentation/media/uapi/dvb/ca.rst

@@ -10,6 +10,11 @@ accessed through ``/dev/dvb/adapter?/ca?``. Data types and and ioctl
 definitions can be accessed by including ``linux/dvb/ca.h`` in your
 application.
 
+.. note::
+
+   There are three ioctls at this API that aren't documented:
+   :ref:`CA_GET_MSG`, :ref:`CA_SEND_MSG` and :ref:`CA_SET_DESCR`.
+   Documentation for them are welcome.
 
 .. toctree::
     :maxdepth: 1

Documentation/media/uapi/dvb/legacy_dvb_apis.rst

@@ -12,6 +12,11 @@ drivers should use it. Instead, audio and video should be using the V4L2
 and ALSA APIs, and the pipelines should be set using the Media
 Controller API
 
+.. note::
+
+   The APIs described here doesn't necessarily reflect the current
+   code implementation.
+
 
 .. toctree::
     :maxdepth: 1