usb: dwc3: meson-g12a: support the GXL/GXM DWC3 host phy disconnect

On the Amlogic GXL/GXM SoCs, the OTG PHY status signals are always
connected to the DWC3 controller, thus crashing the controller when
switching to OTG mode when port is not populated with a device/cable to
Host.

Amlogic added a bit to disconnect the OTG PHY status signals from the DWC3
to be used when switching the OTG PHY as Device to the DWC2 controller.

The drawback is that it makes the DWC3 port state machine stall and needs
a full reset of the DWC3 controller to get connect status to the port
connected to the OTG PHY, but not the other one.

Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>