dt-bindings: iio: adc: ti,adc081c: Document the binding

Linux has a driver for these ADCs at drivers/iio/adc/ti-adc081c.c, but
the compatible strings were undocumented. Add a binding for them. The
hardware has an alert interrupt output, but existing ti,adc081c users
do not provide the 'interrupts' property, so leave it as optional.
Signed-off-by: Samuel Holland <samuel@sholland.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20221125220903.8632-1-samuel@sholland.orgSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/adc/ti,adc081c.yaml

+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/adc/ti,adc081c.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: TI Single-channel I2C ADCs
+
+maintainers:
+  - Jonathan Cameron <jic23@kernel.org>
+  - Lars-Peter Clausen <lars@metafoo.de>
+
+description: |
+  Single-channel ADC supporting 8, 10, or 12-bit samples and high/low alerts.
+
+properties:
+  compatible:
+    enum:
+      - ti,adc081c
+      - ti,adc101c
+      - ti,adc121c
+
+  reg:
+    maxItems: 1
+
+  interrupts:
+    maxItems: 1
+
+  vref-supply:
+    description:
+      Regulator for the combined power supply and voltage reference
+
+  "#io-channel-cells":
+    const: 1
+
+required:
+  - compatible
+  - reg
+  - vref-supply
+
+additionalProperties: false
+
+examples:
+  - |
+    i2c {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        adc@52 {
+            compatible = "ti,adc081c";
+            reg = <0x52>;
+            vref-supply = <&reg_2p5v>;
+        };
+    };
+...