USB: ehci-msm: Add device tree support and binding information

Allows MSM EHCI controller to be specified via device tree.

Signed-off-by: Ivan T. Ivanov <iivanov@mm-sol.com>
Acked-by: David Brown <davidb@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>