[media] doc-rst: Fix conversion for MC core functions

There were lots of issues at the media controller side,
after the conversion:

- Some documentation at the header files weren't using the
  kernel-doc start block;

- Now, the C files with the exported symbols also need to be
  added. So, all headers need to be included twice: one to
  get the structs/enums/.. and another one for the functions;

- Notes should use the ReST tag, as kernel-doc doesn't
  recognizes it anymore;

- Identation needs to be fixed, as ReST uses it to identify
  when a format "tag" ends.

- Fix the cross-references at the media controller description.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>