[media] dvbdev: Add RF connector if needed

Several pure digital TV devices have a frontend with the tuner
integrated on it. Add the RF connector when dvb_create_media_graph()
is called on such devices.

Tested with siano and dvb_usb_mxl111sf drivers.

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