MIPS: BCM47XX: fixup broken MAC addresses in nvram

MIPS: BCM47XX: fixup broken MAC addresses in nvram

The address prefix 00:90:4C is used by Broadcom in their initial
configuration. When a mac address with the prefix 00:90:4C is used all
devices from the same series are sharing the same mac address. To
prevent mac address collisions we replace them with a mac address based
on the base address. To generate such addresses we take the main mac
address from et0macaddr and increase it by two for the first wifi
device and by 3 for the second one. This matches the printed mac
address on the device. The main mac address increased by one is used as
wan address by the vendor code.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Cc: zajec5@gmail.com
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/7489/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>