dt-bindings: iio: potentiometer: Add the Renesas X9250 potentiometers

The Renesas X9250 is a quad digitally controlled potentiometers.
Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230509160852.158101-2-herve.codina@bootlin.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/potentiometer/renesas,x9250.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/potentiometer/renesas,x9250.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Renesas X9250 quad potentiometers
+
+maintainers:
+  - Herve Codina <herve.codina@bootlin.com>
+
+description:
+  The Renesas X9250 integrates four digitally controlled potentiometers.
+  On each potentiometer, the X9250T has a 100 kOhms total resistance and the
+  X9250U has a 50 kOhms total resistance.
+
+allOf:
+  - $ref: /schemas/spi/spi-peripheral-props.yaml
+
+properties:
+  compatible:
+    enum:
+      - renesas,x9250t
+      - renesas,x9250u
+
+  reg:
+    maxItems: 1
+
+  vcc-supply:
+    description:
+      Regulator for the VCC power supply.
+
+  avp-supply:
+    description:
+      Regulator for the analog V+ power supply.
+
+  avn-supply:
+    description:
+      Regulator for the analog V- power supply.
+
+  '#io-channel-cells':
+    const: 1
+
+  spi-max-frequency:
+    maximum: 2000000
+
+  wp-gpios:
+    maxItems: 1
+    description:
+      GPIO connected to the write-protect pin.
+
+required:
+  - compatible
+  - reg
+  - vcc-supply
+  - avp-supply
+  - avn-supply
+  - '#io-channel-cells'
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+    spi {
+        #address-cells = <1>;
+        #size-cells = <0>;
+        potentiometer@0 {
+            compatible = "renesas,x9250t";
+            reg = <0>;
+            vcc-supply = <&vcc_regulator>;
+            avp-supply = <&avp_regulator>;
+            avn-supply = <&avp_regulator>;
+            wp-gpios = <&gpio 1 GPIO_ACTIVE_LOW>;
+            spi-max-frequency = <2000000>;
+            #io-channel-cells = <1>;
+        };
+    };