USB: EHCI: make ehci-w90X900 a separate driver

Separate the W90X900(W90P910) on-chip host controller driver from
ehci-hcd host code so that it can be built as a separate driver module.
This work is part of enabling multi-platform kernels on ARM;
however, note that other changes are still needed before W90X900(W90P910)
can be booted with a multi-platform kernel

and an ehci driver that only works on one of them.

With the infrastructure added by Alan Stern in patch 3e023203
"USB: EHCI: prepare to make ehci-hcd a library module", we can
avoid this problem by turning a bus glue into a separate
module, as we do here for the w90X900 bus glue.

This patch is rebased on greghk/usb-next 3.12 rc1.

Signed-off-by: Manjunath Goudar <manjunath.goudar@linaro.org>
Signed-off-by: Deepak Saxena <dsaxena@linaro.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Wan ZongShun <mcuos.com@gmail.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>