[media] docs-rst: improve the kAPI documentation for the mediactl

There are several issues on the documentation:
  - the media.h header were not properly referenced;
  - verbatim expressions were not properly marked as such;
  - struct member references were wrong;
  - some notes were not using the right markup;
  - a comment that were moved to the kernel-doc markup were
    duplicated as a comment inside the struct media_entity;
  - some args were not pointing to the struct they're using;
  - macros weren't documented.

Signed-off-by: Mauro Carvalho Chehab <[email protected]>
diff --git a/include/media/media-devnode.h b/include/media/media-devnode.h
index 37d4948..972168e 100644
--- a/include/media/media-devnode.h
+++ b/include/media/media-devnode.h
@@ -75,7 +75,7 @@
  * @cdev:	struct cdev pointer character device
  * @parent:	parent device
  * @minor:	device node minor number
- * @flags:	flags, combination of the MEDIA_FLAG_* constants
+ * @flags:	flags, combination of the ``MEDIA_FLAG_*`` constants
  * @release:	release callback called at the end of media_devnode_release()
  *
  * This structure represents a media-related device node.