dt-bindings: iio: adc: document qcom-spmi-rradc

Add dt-binding docs for the Qualcomm SPMI RRADC found in PMICs like
PMI8998 and PMI8994
Signed-off-by: Caleb Connolly <caleb.connolly@linaro.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220429220904.137297-5-caleb.connolly@linaro.orgSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/adc/qcom,spmi-rradc.yaml

+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/adc/qcom,spmi-rradc.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Qualcomm's SPMI PMIC Round Robin ADC
+
+maintainers:
+  - Caleb Connolly <caleb.connolly@linaro.org>
+
+description: |
+  The Qualcomm SPMI Round Robin ADC (RRADC) provides interface to clients to
+  read the voltage, current and temperature for supported peripherals such as
+  the battery thermistor die temperature, charger temperature, USB and DC input
+  voltage / current and battery ID resistor.
+
+properties:
+  compatible:
+    enum:
+      - qcom,pmi8998-rradc
+      - qcom,pm660-rradc
+
+  reg:
+    maxItems: 1
+
+  qcom,batt-id-delay-ms:
+    description: Sets the hardware settling time for the battery ID resistor.
+    enum: [0, 1, 4, 12, 20, 40, 60, 80]
+
+  "#io-channel-cells":
+    const: 1
+
+required:
+  - compatible
+  - reg
+
+additionalProperties: false
+
+examples:
+  - |
+    pmic {
+      #address-cells = <1>;
+      #size-cells = <0>;
+
+      pmic_rradc: adc@4500 {
+          compatible = "qcom,pmi8998-rradc";
+          reg = <0x4500>;
+          #io-channel-cells  = <1>;
+      };
+    };