dt-bindings: iio: ti,ads8688 yaml conversion

Fairly simple binding.  Most of the changes were filling in information
not previously found in the binding.  I dropped the previous explicit
mention of spi-max-frequency as that is covered by the generic SPI
binding.
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Acked-by: Sean Nyekjaer <sean@geanix.com>
Reviewed-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/iio/adc/ti,ads8688.yaml

+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/adc/ti,ads8688.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Texas Instruments' ADS8684 and ADS8688 ADC chip
+
+maintainers:
+  - Sean Nyekjaer <sean@geanix.com>
+
+description: |
+   SPI 16bit ADCs with 4/8 channels.
+
+properties:
+  compatible:
+    enum:
+      - ti,ads8684
+      - ti,ads8688
+
+  reg:
+    maxItems: 1
+
+  vref-supply:
+    description: Optional external reference.  If not supplied, assume
+      REFSEL input tied low to enable the internal reference.
+
+required:
+  - compatible
+  - reg
+
+examples:
+  - |
+    spi {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        adc@0 {
+            compatible = "ti,ads8688";
+            reg = <0>;
+            vref-supply = <&vdd_supply>;
+            spi-max-frequency = <1000000>;
+        };
+    };
+...

Documentation/devicetree/bindings/iio/adc/ti-ads8688.txt

-* Texas Instruments' ADS8684 and ADS8688 ADC chip
-
-Required properties:
- - compatible: Should be "ti,ads8684" or "ti,ads8688"
- - reg: spi chip select number for the device
-
-Recommended properties:
- - spi-max-frequency: Definition as per
-		Documentation/devicetree/bindings/spi/spi-bus.txt
-
-Optional properties:
- - vref-supply: The regulator supply for ADC reference voltage
-
-Example:
-adc@0 {
-	compatible = "ti,ads8688";
-	reg = <0>;
-	vref-supply = <&vdd_supply>;
-	spi-max-frequency = <1000000>;
-};