staging: dwc2: add platform device bindings

This adds a dwc_platform.ko module that can be loaded by using
compatible = "snps,dwc2" in a device tree.

Signed-off-by: Matthijs Kooijman <matthijs@stdin.nl>
Signed-off-by: Paul Zimmerman <paulz@synopsys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>