phy: amlogic: meson-gxl-usb3: remove code for non-existing PHY

The registers which are managed by the meson-gxl-usb3 PHY driver are
actually "USB control" registers (which are "glue" registers which
manage OTG detection and routing of the OTG capable port between the
DWC2 peripheral-only controller and the DWC3 host-only controller).

Drop the meson-gxl-usb3 PHY driver now that the dwc3-meson-g12a-usb
driver supports the USB control registers on GXL and GXM SoCs (these
were previously managed by the meson-gxl-usb3 PHY driver).

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