dt-bindings: usb: dwc2: Add Amlogic G12A DWC2 Compatible

Adds the specific compatible string for the DWC2 IP found in the
Amlogic G12A SoC Family.
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

Documentation/devicetree/bindings/usb/dwc2.txt

@@ -14,6 +14,7 @@ Required properties:
   - "amlogic,meson8-usb": The DWC2 USB controller instance in Amlogic Meson8 SoCs;
   - "amlogic,meson8b-usb": The DWC2 USB controller instance in Amlogic Meson8b SoCs;
   - "amlogic,meson-gxbb-usb": The DWC2 USB controller instance in Amlogic S905 SoCs;
+  - "amlogic,meson-g12a-usb": The DWC2 USB controller instance in Amlogic G12A SoCs;
   - "amcc,dwc-otg": The DWC2 USB controller instance in AMCC Canyonlands 460EX SoCs;
   - snps,dwc2: A generic DWC2 USB controller with default parameters.
   - "st,stm32f4x9-fsotg": The DWC2 USB FS/HS controller instance in STM32F4x9 SoCs