dt-bindings: serial: samsung: Add 'power-domains' property

Some Samsung UARTs are in a power domain, so allow 'power-domains'
property.
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220823145649.3118479-1-robh@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/serial/samsung_uart.yaml

@@ -68,6 +68,9 @@ properties:
     minItems: 1
     maxItems: 2
 
+  power-domains:
+    maxItems: 1
+
   samsung,uart-fifosize:
     description: The fifo size supported by the UART channel.
     $ref: /schemas/types.yaml#/definitions/uint32