media: dvb uapi docs: better organize header files

Instead of having one chapter per file, place all of them at
the same chapter. That better organize the chapters at the uAPI
documentation.

As a side effect, now all uAPI headers are at the same page,
at the html output, with makes easier to use it as a reference
index for the spec.

Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

Documentation/media/uapi/dvb/audio_h.rst

···
-.. -*- coding: utf-8; mode: rst -*-
-
-.. _audio_h:
-
-*********************
-DVB Audio Header File
-*********************
-
-.. kernel-include:: $BUILDDIR/audio.h.rst

Documentation/media/uapi/dvb/ca_h.rst

···
-.. -*- coding: utf-8; mode: rst -*-
-
-.. _ca_h:
-
-**********************************
-DVB Conditional Access Header File
-**********************************
-
-.. kernel-include:: $BUILDDIR/ca.h.rst

Documentation/media/uapi/dvb/dmx_h.rst

···
-.. -*- coding: utf-8; mode: rst -*-
-
-.. _dmx_h:
-
-*********************
-DVB Demux Header File
-*********************
-
-.. kernel-include:: $BUILDDIR/dmx.h.rst

Documentation/media/uapi/dvb/dvbapi.rst

···
     net
     legacy_dvb_apis
     examples
-    audio_h
-    ca_h
-    dmx_h
-    frontend_h
-    net_h
-    video_h
+    headers
 
 
 **********************

Documentation/media/uapi/dvb/frontend_h.rst

···
-.. -*- coding: utf-8; mode: rst -*-
-
-.. _frontend_h:
-
-************************
-DVB Frontend Header File
-************************
-
-.. kernel-include:: $BUILDDIR/frontend.h.rst

Documentation/media/uapi/dvb/headers.rst

···
+****************************
+Digital TV uAPI header files
+****************************
+
+Digital TV uAPI headers
+***********************
+
+.. kernel-include:: $BUILDDIR/frontend.h.rst
+
+.. kernel-include:: $BUILDDIR/dmx.h.rst
+
+.. kernel-include:: $BUILDDIR/ca.h.rst
+
+.. kernel-include:: $BUILDDIR/net.h.rst
+
+Legacy uAPI
+***********
+
+.. kernel-include:: $BUILDDIR/audio.h.rst
+
+.. kernel-include:: $BUILDDIR/video.h.rst

Documentation/media/uapi/dvb/net_h.rst

···
-.. -*- coding: utf-8; mode: rst -*-
-
-.. _net_h:
-
-***********************
-DVB Network Header File
-***********************
-
-.. kernel-include:: $BUILDDIR/net.h.rst

Documentation/media/uapi/dvb/video_h.rst

···
-.. -*- coding: utf-8; mode: rst -*-
-
-.. _video_h:
-
-*********************
-DVB Video Header File
-*********************
-
-.. kernel-include:: $BUILDDIR/video.h.rst