[media] docs-rst: media: Push CEC documentation under CEC section

The CEC documentation added two sections on the main media kAPI level.
There should be only one.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

Documentation/media/kapi/cec-core.rst

@@ -27,11 +27,8 @@ HDMI 1.3a specification is sufficient:
 http://www.microprocessor.org/HDMISpecification13a.pdf
 
 
-The Kernel Interface
-====================
-
-CEC Adapter
------------
+CEC Adapter Interface
+---------------------
 
 The struct cec_adapter represents the CEC adapter hardware. It is created by
 calling cec_allocate_adapter() and deleted by calling cec_delete_adapter():