dm: usb: Allow setting up a USB controller as a device/gadget

dm: usb: Allow setting up a USB controller as a device/gadget

Some controllers support OTG (on-the-go) where they can operate as either
host or device. The gadget layer in U-Boot supports this.

While this layer does not interact with driver model, we can provide a
function which sets up the controller in the correct way. This way the code
at least builds (although it likely will not work).

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Marek Vasut <marex@denx.de>