dt-bindings: msm/dsi: Add mdp transfer time to msm dsi binding

Optional properties:

- qcom,dsi-phy-regulator-ldo-mode: Boolean value indicating if the LDO mode PHY

  regulator is wanted.

- qcom,mdss-mdp-transfer-time-us:	Specifies the dsi transfer time for command mode

					panels in microseconds. Driver uses this number to adjust

					the clock rate according to the expected transfer time.

					Increasing this value would slow down the mdp processing

					and can result in slower performance.

					Decreasing this value can speed up the mdp processing,

					but this can also impact power consumption.

					As a rule this time should not be higher than the time

					that would be expected with the processing at the

					dsi link rate since anyways this would be the maximum

					transfer time that could be achieved.

					If ping pong split is enabled, this time should not be higher

					than two times the dsi link rate time.

					If the property is not specified, then the default value is 14000 us.

[1] Documentation/devicetree/bindings/clock/clock-bindings.txt

[2] Documentation/devicetree/bindings/graph.txt

		qcom,master-dsi;

		qcom,sync-dual-dsi;

		qcom,mdss-mdp-transfer-time-us = <12000>;

		pinctrl-names = "default", "sleep";

		pinctrl-0 = <&dsi_active>;

		pinctrl-1 = <&dsi_suspend>;