dt-bindings: iio: adc: maxim,max1118 yaml conversion

Simple device with a simple conversion.  Special handling needed
for the max1118 which is the only supported part that has an external
reference voltage.

Cc: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/iio/adc/max1118.txt

-* MAX1117/MAX1118/MAX1119 8-bit, dual-channel ADCs
-
-Required properties:
- - compatible: Should be one of
-	* "maxim,max1117"
-	* "maxim,max1118"
-	* "maxim,max1119"
- - reg: spi chip select number for the device
- - (max1118 only) vref-supply: The regulator supply for ADC reference voltage
-
-Recommended properties:
- - spi-max-frequency: Definition as per
-		Documentation/devicetree/bindings/spi/spi-bus.txt
-
-Example:
-adc@0 {
-	compatible = "maxim,max1118";
-	reg = <0>;
-	vref-supply = <&vdd_supply>;
-	spi-max-frequency = <1000000>;
-};

Documentation/devicetree/bindings/iio/adc/maxim,max1118.yaml

+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/adc/maxim,max1118.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Maxim MAX1118 and similar ADCs
+
+maintainers:
+  - Akinobu Mita <akinobu.mita@gmail.com>
+
+description: |
+    Dual channel 8bit ADCs.
+
+properties:
+  compatible:
+    enum:
+      - maxim,max1117
+      - maxim,max1118
+      - maxim,max1119
+
+  reg:
+    maxItems: 1
+
+  spi-max-frequency:
+    maximum: 5000000
+
+  vref-supply:
+    description: External reference, needed to establish input scaling
+
+if:
+  properties:
+    compatible:
+      contains:
+        const: maxim,max1118
+then:
+  required:
+    - vref-supply
+else:
+  properties:
+    vref-supply: false
+
+required:
+  - compatible
+  - reg
+
+additionalProperties: false
+
+examples:
+  - |
+    spi {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        adc@0 {
+            compatible = "maxim,max1118";
+            reg = <0>;
+            vref-supply = <&adc_vref>;
+            spi-max-frequency = <1000000>;
+        };
+    };
+...