dt-bindings: phy: samsung,usb2-phy: convert to dtschema

Convert the Samsung SoC USB 2.0 PHY bindings to DT schema format.

Except the conversion, add also vbus-supply property which was already
used by the driver and DTS.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220129193646.372481-5-krzysztof.kozlowski@canonical.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>