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

Allows the OMAP EHCI controller to be specified via device tree.

Signed-off-by: Roger Quadros <rogerq@ti.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>