dt-bindings: mmc: rockchip-dw-mshc: Add power-domains property

Document power-domains property in rockchip dw controller.

RV1126 is using eMMC and SDIO power domains but SDMMC is not.

Signed-off-by: Jagan Teki <jagan@edgeble.ai>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20221108041400.157052-3-jagan@edgeble.ai
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Documentation/devicetree/bindings/mmc/rockchip-dw-mshc.yaml

@@ -71,6 +71,9 @@ properties:
       to control the clock phases, "ciu-sample" is required for tuning
       high speed modes.
 
+  power-domains:
+    maxItems: 1
+
   rockchip,default-sample-phase:
     $ref: /schemas/types.yaml#/definitions/uint32
     minimum: 0