usb: dwc2: Deprecate g-use-dma binding

This is not needed as the gadget now fully supports DMA and it can
autodetect it. This was initially added because gadget DMA mode was only
partially implemented so could not be automatically enabled.

Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>