Add bus dependent revision read function which is used to
determine chipset's MAC before hardware is initialized.
Signed-off-by: NFelix Fietkau <nbd@openwrt.org>
Signed-off-by: NWojciech Dubowik <Wojciech.Dubowik@neratec.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>