dt-bindings: iio: adc: add bindings doc for AXI ADC driver

This change adds the bindings documentation for the AXI ADC driver.
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/adc/adi,axi-adc.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/adc/adi,axi-adc.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Analog Devices AXI ADC IP core
+
+maintainers:
+  - Michael Hennerich <michael.hennerich@analog.com>
+  - Alexandru Ardelean <alexandru.ardelean@analog.com>
+
+description: |
+  Analog Devices Generic AXI ADC IP core for interfacing an ADC device
+  with a high speed serial (JESD204B/C) or source synchronous parallel
+  interface (LVDS/CMOS).
+  Usually, some other interface type (i.e SPI) is used as a control
+  interface for the actual ADC, while this IP core will interface
+  to the data-lines of the ADC and handle the streaming of data into
+  memory via DMA.
+
+  https://wiki.analog.com/resources/fpga/docs/axi_adc_ip
+
+properties:
+  compatible:
+    enum:
+      - adi,axi-adc-10.0.a
+
+  reg:
+    maxItems: 1
+
+  dmas:
+    maxItems: 1
+
+  dma-names:
+    items:
+      - const: rx
+
+  adi,adc-dev:
+    $ref: /schemas/types.yaml#/definitions/phandle
+    description:
+      A reference to a the actual ADC to which this FPGA ADC interfaces to.
+
+required:
+  - compatible
+  - dmas
+  - reg
+  - adi,adc-dev
+
+additionalProperties: false
+
+examples:
+  - |
+    axi-adc@44a00000 {
+          compatible = "adi,axi-adc-10.0.a";
+          reg = <0x44a00000 0x10000>;
+          dmas = <&rx_dma 0>;
+          dma-names = "rx";
+
+          adi,adc-dev = <&spi_adc>;
+    };
+...