[media] docs-rst: move cec kAPI documentation to the media book

The CEC kAPI documentation should also be part of the media book.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
diff --git a/Documentation/media/media_kapi.rst b/Documentation/media/media_kapi.rst
index b71e8e8..f282ca2 100644
--- a/Documentation/media/media_kapi.rst
+++ b/Documentation/media/media_kapi.rst
@@ -32,3 +32,4 @@
     kapi/dtv-core
     kapi/rc-core
     kapi/mc-core
+    kapi/cec-core