dt-bindings: serial: cdsn,uart: add power-domains

Few Xilinx DTS have power domains in serial node:

  zynqmp-zc1232-revA.dtb: serial@ff000000: Unevaluated properties are not allowed ('power-domains' was unexpected)

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Michal Simek <michal.simek@amd.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230124091916.45054-3-krzysztof.kozlowski@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/serial/cdns,uart.yaml

@@ -9,9 +9,6 @@ title: Cadence UART Controller
 maintainers:
   - Michal Simek <michal.simek@xilinx.com>
 
-allOf:
-  - $ref: serial.yaml#
-
 properties:
   compatible:
     oneOf:
@@ -46,6 +43,9 @@ properties:
       port does not use this pin.
     type: boolean
 
+  power-domains:
+    maxItems: 1
+
 required:
   - compatible
   - reg
@@ -53,6 +53,17 @@ required:
   - clocks
   - clock-names
 
+allOf:
+  - $ref: serial.yaml#
+  - if:
+      properties:
+        compatible:
+          contains:
+            const: cdns,uart-r1p8
+    then:
+      properties:
+        power-domains: false
+
 unevaluatedProperties: false
 
 examples: