dt-bindings: serial: qcom,msm-uartdm: convert to dtschema

Convert the Qualcomm MSM Serial UARTDM bindings to DT Schema.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220405063451.12011-8-krzysztof.kozlowski@linaro.org