[PATCH] sb1250-mac: Add support for the BCM1480

This adds support for the 4th port and other new features of the
BCM1480 SOC.

Signed-Off-By: Andy Isaacson <adi@broadcom.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>