[media] DocBook: Better organize media devices

Instead of putting all media devices on a flat structure,
split them on 4 types, just like we do with the userspace API:
	Video2Linux devices
	Digital TV (DVB) devices
	Remote Controller devices
	Media Controller devices

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
Acked-by: Jonathan Corbet <corbet@lwn.net>