dt-bindings: usb: dwc2: Document quirk to reset PHY upon wakeup

On Rockchip rk3288 there's a hardware quirk where we need to assert
the reset signal to the PHY when we get a remote wakeup on one of the
two ports.  Document this quirk in the bindings.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>