Driver Core: raw: add nodename for raw devices

This adds support to the raw driver to report the proper device name to
userspace for the raw 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>