dt-bindings: msm: dsi-controller-main: Move power-domain to individual compatible properties

power-domains is not a required property for older qcom parts. From review
of the available dts it appears the dependency starts around about sdm630.

Move the property to the silicon parts that require it only.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>