usb: dwc3: of-simple: Add compatible for Allwinner H6 platform

Add compatible string to use this generic glue layer to support
Allwinner H6 platform's dwc3 controller.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>