dt-bindings: clock: qcom,gcc-sc7180: document CX power domain

The GCC clock controller needs CX power domain, at least according to
DTS:

  sc7180-trogdor-pompom-r3.dtb: clock-controller@100000: Unevaluated properties are not allowed ('power-domains' was unexpected)
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230516105241.30091-2-krzysztof.kozlowski@linaro.org

Documentation/devicetree/bindings/clock/qcom,gcc-sc7180.yaml

@@ -32,6 +32,10 @@ properties:
       - const: bi_tcxo_ao
       - const: sleep_clk
 
+  power-domains:
+    items:
+      - description: CX domain
+
 required:
   - compatible
   - clocks
@@ -45,6 +49,8 @@ unevaluatedProperties: false
 examples:
   - |
     #include <dt-bindings/clock/qcom,rpmh.h>
+    #include <dt-bindings/power/qcom-rpmpd.h>
+
     clock-controller@100000 {
       compatible = "qcom,gcc-sc7180";
       reg = <0x00100000 0x1f0000>;
@@ -52,6 +58,7 @@ examples:
                <&rpmhcc RPMH_CXO_CLK_A>,
                <&sleep_clk>;
       clock-names = "bi_tcxo", "bi_tcxo_ao", "sleep_clk";
+      power-domains = <&rpmhpd SC7180_CX>;
       #clock-cells = <1>;
       #reset-cells = <1>;
       #power-domain-cells = <1>;