[SSB]: add Sonics Silicon Backplane bus support

SSB is an SoC bus used in a number of embedded devices.  The most
well-known of these devices is probably the Linksys WRT54G, but there
are others as well.  The bus is also used internally on the BCM43xx
and BCM44xx devices from Broadcom.

This patch also includes support for SSB ID tables in modules, so
that SSB drivers can be loaded automatically.

Signed-off-by: Michael Buesch <mb@bu3sch.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>