[media] dvb-usb-v2: add support for the media controller at USB driver

Create a struct media_device and add it to the dvb adapter.

Please notice that the tuner is not mapped yet by the dvb core.

[mchehab@osg.samsung.com: use config option MEDIA_CONTROLLER_DVB due to a rebase]
Signed-off-by: Rafael Lourenço de Lima Chehab <chehabrafael@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>