dt-bindings: phy: add QMP USB PHY schema

The QMP PHY DT schema is getting unwieldy. Break out the USB PHY
binding in a separate file.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Link: https://lore.kernel.org/r/20220830112923.3725-20-johan+linaro@kernel.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>