media: dtv-demux.rst: parse other demux headers with kernel-doc

Now that we have kernel-doc markups at dvb_demux.h and dmxdev.h,
parse them.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

Documentation/media/kapi/dtv-demux.rst

@@ -66,7 +66,17 @@ function call directly from a hardware interrupt.
 This mechanism is implemented by :c:func:`dmx_ts_cb()` and :c:func:`dmx_section_cb()`
 callbacks.
 
-Digital TV Demux functions and types
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Digital TV Demux device registration functions and data structures
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. kernel-doc:: drivers/media/dvb-core/dmxdev.h
+
+High-level Digital TV demux interface
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. kernel-doc:: drivers/media/dvb-core/dvb_demux.h
+
+Driver-internal low-level hardware specific driver demux interface
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 .. kernel-doc:: drivers/media/dvb-core/demux.h