w1: introduce helper to generate mac address from 1-wire id
use the first 3 byte of the id of a 1-wire
or 6 if no OUI provided device to provide an Ethernet address
Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>