ssb: Add Gigabit Ethernet driver

This adds the Gigabit Ethernet driver for the SSB
Gigabit Ethernet core. This driver actually is a frontend to
the Tigon3 driver. So the real work is done by tg3.
This device is used in the Linksys WRT350N.

Signed-off-by: Michael Buesch <mb@bu3sch.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>