dt-bindings: phy: convert meson-gxl-usb2-phy.txt to dt-schema

Convert the Amlogic Meson GXL USB2 PHY bindings to dt-schema.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20221117-b4-amlogic-bindings-convert-v2-8-36ad050bb625@linaro.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>