dt-bindings: usb: amlogic,meson-g12a-usb-ctrl: add the Amlogic AXG Families USB Glue Bindings

The Amlogic AXG is close to the GXL Glue but with a single OTG PHY.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Kevin Hilman <khilman@baylibre.com>
Acked-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>