dt-bindings:iio:dac: add ad7293 doc

Add device tree bindings for the AD7293 Power Amplifier.
Signed-off-by: Antoniu Miclaus <antoniu.miclaus@analog.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20211202150819.24832-2-antoniu.miclaus@analog.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/dac/adi,ad7293.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/dac/adi,ad7293.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: AD7293 12-Bit Power Amplifier Current Controller with ADC,
+       DACs, Temperature and Current Sensors
+
+maintainers:
+  - Antoniu Miclaus <antoniu.miclaus@analog.com>
+
+description: |
+   Power Amplifier drain current controller containing functionality
+   for general-purpose monitoring and control of current, voltage,
+   and temperature, integrated into a single chip solution with an
+   SPI-compatible interface.
+
+   https://www.analog.com/en/products/ad7293.html
+
+properties:
+  compatible:
+    enum:
+      - adi,ad7293
+
+  avdd-supply: true
+
+  vdrive-supply: true
+
+  reset-gpios:
+    maxItems: 1
+
+  reg:
+    maxItems: 1
+
+  spi-max-frequency:
+    maximum: 1000000
+
+required:
+  - compatible
+  - reg
+  - avdd-supply
+  - vdrive-supply
+
+additionalProperties: false
+
+examples:
+  - |
+    spi {
+      #address-cells = <1>;
+      #size-cells = <0>;
+      ad7293@0 {
+        compatible = "adi,ad7293";
+        reg = <0>;
+        spi-max-frequency = <1000000>;
+        avdd-supply = <&avdd>;
+        vdrive-supply = <&vdrive>;
+        reset-gpios = <&gpio 10 0>;
+      };
+    };
+...