usb: dwc-meson-g12a: Add support for USB on AXG SoCs
The Amlogic AXG is close to the GXL Glue but with a single OTG PHY.
It needs the same init sequence as GXL & GXM, but it seems it doesn't need
the host disconnect bit.
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com> Signed-off-by: Neil Armstrong <narmstrong@baylibre.com> Reviewed-by: Kevin Hilman <khilman@baylibre.com> Signed-off-by: Felipe Balbi <balbi@kernel.org>