dt-bindings: iio: adc: ad7923: Add binding documentation for AD7928

This patch add device tree binding documentation for AD7923 adc in YAML
format.
Signed-off-by: Daniel Junho <djunho@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/adc/adi,ad7923.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/adc/adi,ad7923.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Analog Devices AD7923 and similars with 4 and 8 Channel ADCs.
+
+maintainers:
+  - Michael Hennerich <michael.hennerich@analog.com>
+  - Patrick Vasseur <patrick.vasseur@c-s.fr>
+
+description: |
+  Analog Devices AD7904, AD7914, AD7923, AD7924 4 Channel ADCs, and AD7908,
+   AD7918, AD7928 8 Channels ADCs.
+
+  Specifications about the part can be found at:
+    https://www.analog.com/media/en/technical-documentation/data-sheets/AD7923.pdf
+    https://www.analog.com/media/en/technical-documentation/data-sheets/AD7904_7914_7924.pdf
+    https://www.analog.com/media/en/technical-documentation/data-sheets/AD7908_7918_7928.pdf
+
+properties:
+  compatible:
+    enum:
+      - adi,ad7904
+      - adi,ad7914
+      - adi,ad7923
+      - adi,ad7924
+      - adi,ad7908
+      - adi,ad7918
+      - adi,ad7928
+
+  reg:
+    maxItems: 1
+
+  refin-supply:
+    description: |
+      The regulator supply for ADC reference voltage.
+
+  '#address-cells':
+    const: 1
+
+  '#size-cells':
+    const: 0
+
+required:
+  - compatible
+  - reg
+
+examples:
+  - |
+    spi {
+      #address-cells = <1>;
+      #size-cells = <0>;
+
+      ad7928: adc@0 {
+        compatible = "adi,ad7928";
+        reg = <0>;
+        spi-max-frequency = <25000000>;
+        refin-supply = <&adc_vref>;
+
+        #address-cells = <1>;
+        #size-cells = <0>;
+      };
+    };