[MIPS] tc35815: Load MAC address via platform_device

TX49XX SoCs include PCI NIC (TC35815 compatible) connected via its
internal PCI bus, but the NIC's PROM interface is not connected to
SEEPROM.  So we must provide its ethernet address by another way.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Acked-by: Jeff Garzik <jeff@garzik.org>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>