media: docs: move uAPI book to userspace-api/media

Since 2017, there is an space reserved for userspace API,
created by changeset 1d596dee38 ("docs: Create a user-space API guide").

As the media subsystem was one of the first subsystems to use
Sphinx, until this patch, we were keeping things on a separate
place.

Let's just use the new location, as having all uAPI altogether
will likely make things easier for developers.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Documentation/userspace-api/media/dvb/audio-stop.rst

@@ -0,0 +1,56 @@
+.. Permission is granted to copy, distribute and/or modify this
+.. document under the terms of the GNU Free Documentation License,
+.. Version 1.1 or any later version published by the Free Software
+.. Foundation, with no Invariant Sections, no Front-Cover Texts
+.. and no Back-Cover Texts. A copy of the license is included at
+.. Documentation/userspace-api/media/fdl-appendix.rst.
+..
+.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
+
+.. _AUDIO_STOP:
+
+==========
+AUDIO_STOP
+==========
+
+Name
+----
+
+AUDIO_STOP
+
+.. attention:: This ioctl is deprecated
+
+Synopsis
+--------
+
+.. c:function:: int ioctl(int fd, AUDIO_STOP)
+    :name: AUDIO_STOP
+
+Arguments
+---------
+
+.. flat-table::
+    :header-rows:  0
+    :stub-columns: 0
+
+
+    -  .. row 1
+
+       -  int fd
+
+       -  File descriptor returned by a previous call to open().
+
+
+Description
+-----------
+
+This ioctl call asks the Audio Device to stop playing the current
+stream.
+
+
+Return Value
+------------
+
+On success 0 is returned, on error -1 and the ``errno`` variable is set
+appropriately. The generic error codes are described at the
+:ref:`Generic Error Codes <gen-errors>` chapter.