Driver Core: dvb: add nodename for dvb drivers

This adds support to the dvb core to report the proper device name to
userspace for their devices.

Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Jan Blunck <jblunck@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>