[media] doc-rst: add media.h header to media contrller

Adding the header file is interesting for several reasons:

1) It makes MC documentation consistend with other parts;
2) The header file can be used as a quick index to all API
   elements;
3) The cross-reference check helps to identify symbols that
   aren't documented.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
diff --git a/Documentation/media/uapi/mediactl/media-ioc-enum-entities.rst b/Documentation/media/uapi/mediactl/media-ioc-enum-entities.rst
index ae88f46..12d4b25 100644
--- a/Documentation/media/uapi/mediactl/media-ioc-enum-entities.rst
+++ b/Documentation/media/uapi/mediactl/media-ioc-enum-entities.rst
@@ -1,6 +1,6 @@
 .. -*- coding: utf-8; mode: rst -*-
 
-.. _media-ioc-enum-entities:
+.. _media_ioc_enum_entities:
 
 *****************************
 ioctl MEDIA_IOC_ENUM_ENTITIES
@@ -39,6 +39,8 @@
 structure. The driver fills the rest of the structure or returns an
 EINVAL error code when the id is invalid.
 
+.. _media-ent-id-flag-next:
+
 Entities can be enumerated by or'ing the id with the
 ``MEDIA_ENT_ID_FLAG_NEXT`` flag. The driver will return information
 about the entity with the smallest id strictly larger than the requested