dt-bindings: phy: st: convert phy-stih407-usb to DT schema

Convert the st,stih407-usb2-phy binding to DT schema format.

Signed-off-by: Raphael Gallais-Pou <rgallaispou@gmail.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230823132224.111326-1-rgallaispou@gmail.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>