USB: Add driver for the ssb bus

This adds a USB driver using the generic platform device driver for the
USB controller found on the Broadcom ssb bus. The ssb bus just
exposes one device which serves the OHCI and the EHCI controller at the
same time. This driver probes for this USB controller and creates and
registers two new platform devices which will be probed by the new
generic platform device driver. This makes it possible to use the EHCI
and the OCHI controller on the ssb bus at the same time.

The old ssb OHCI USB driver will be removed in the next step as this
driver also provide an OHCI driver and an EHCI for the cores supporting
it.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>