dt-bindings:iio:adc:adi,ad7949 yaml conversion

Simple SPI driver. I've added the #io-channel-cells
as an optional parameter to allow use of this device as a provider
of ADC capabilities to other devices.
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Cc: Charles-Antoine Couret <charles-antoine.couret@essensium.com>
Link: https://lore.kernel.org/r/20200909175946.395313-15-jic23@kernel.org

Documentation/devicetree/bindings/iio/adc/ad7949.txt

-* Analog Devices AD7949/AD7682/AD7689
-
-Required properties:
- - compatible: Should be one of
-	* "adi,ad7949"
-	* "adi,ad7682"
-	* "adi,ad7689"
- - reg: spi chip select number for the device
- - vref-supply: The regulator supply for ADC reference voltage
-
-Example:
-adc@0 {
-	compatible = "adi,ad7949";
-	reg = <0>;
-	vref-supply = <&vdd_supply>;
-};

Documentation/devicetree/bindings/iio/adc/adi,ad7949.yaml

+# SPDX-License-Identifier: GPL-2.0
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/adc/adi,ad7949.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Analog Devices AD7949/AD7682/AD7689 analog to digital converters
+
+maintainers:
+  - Charles-Antoine Couret <charles-antoine.couret@essensium.com>
+
+description: |
+  Specifications on the converters can be found at:
+    AD7949:
+      https://www.analog.com/media/en/technical-documentation/data-sheets/AD7949.pdf
+    AD7682/AD7698:
+      https://www.analog.com/media/en/technical-documentation/data-sheets/AD7682_7689.pdf
+
+properties:
+  compatible:
+    enum:
+      - adi,ad7682
+      - adi,ad7689
+      - adi,ad7949
+
+  reg:
+    maxItems: 1
+
+  vref-supply:
+    description:
+      ADC reference voltage supply
+
+  spi-max-frequency: true
+
+  "#io-channel-cells":
+    const: 1
+
+required:
+  - compatible
+  - reg
+  - vref-supply
+
+additionalProperties: false
+
+examples:
+  - |
+    spi {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        adc@0 {
+            compatible = "adi,ad7949";
+            reg = <0>;
+            vref-supply = <&vdd_supply>;
+        };
+    };
+...