dt-bindings: iio: adc: amlogic,meson-saradc: add optional power-domains

On newer SoCs, the SAR ADC hardware can require a power-domain to operate,
add it as optional.
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20240605-topic-amlogic-upstream-bindings-fixes-power-domains-sardac-v1-1-40a8de6baa59@linaro.orgSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/adc/amlogic,meson-saradc.yaml

@@ -66,6 +66,9 @@ properties:
   nvmem-cell-names:
     const: temperature_calib
 
+  power-domains:
+    maxItems: 1
+
 allOf:
   - if:
       properties: