USB: EHCI: Add a generic platform device driver

This adds a generic driver for platform devices. It works like the PCI
driver and is based on it. This is for devices which do not have an own
bus but their EHCI controller works like a PCI controller. It will be
used for the Broadcom bcma and ssb USB EHCI controller.

Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>