dt-bindings:iio:adc:x-powers,axp209-adc: txt to yaml conversion

This is a very small binding.  It might make sense at some stage
to just roll it into the parent mfd.  For now, converted as is.
The main advantage of this document is the identification of the
channel index values when this is used as a provider of ADC channels
to consumers.
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20201031184854.745828-32-jic23@kernel.org

Documentation/devicetree/bindings/iio/adc/axp20x_adc.txt

-* X-Powers AXP ADC bindings
-
-Required properties:
-  - compatible: should be one of:
-    - "x-powers,axp209-adc",
-    - "x-powers,axp221-adc",
-    - "x-powers,axp813-adc",
-  - #io-channel-cells: should be 1,
-
-Example:
-
-&axp22x {
-	adc {
-		compatible = "x-powers,axp221-adc";
-		#io-channel-cells = <1>;
-	};
-};
-
-ADC channels and their indexes per variant:
-
-AXP209
-------
- 0 | acin_v
- 1 | acin_i
- 2 | vbus_v
- 3 | vbus_i
- 4 | pmic_temp
- 5 | gpio0_v
- 6 | gpio1_v
- 7 | ipsout_v
- 8 | batt_v
- 9 | batt_chrg_i
-10 | batt_dischrg_i
-
-AXP22x
-------
- 0 | pmic_temp
- 1 | batt_v
- 2 | batt_chrg_i
- 3 | batt_dischrg_i
-
-AXP813
-------
- 0 | pmic_temp
- 1 | gpio0_v
- 2 | batt_v
- 3 | batt_chrg_i
- 4 | batt_dischrg_i

Documentation/devicetree/bindings/iio/adc/x-powers,axp209-adc.yaml

+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/adc/x-powers,axp209-adc.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: X-Powers AXP ADC bindings
+
+maintainers:
+  - Chen-Yu Tsai <wens@csie.org>
+
+description: |
+  ADC is frequently used as a provider to consumers of the ADC channels.
+  Device is a child of an axp209 multifunction device
+  ADC channels and their indexes per variant:
+
+  AXP209
+  ------
+   0 | acin_v
+   1 | acin_i
+   2 | vbus_v
+   3 | vbus_i
+   4 | pmic_temp
+   5 | gpio0_v
+   6 | gpio1_v
+   7 | ipsout_v
+   8 | batt_v
+   9 | batt_chrg_i
+  10 | batt_dischrg_i
+
+  AXP22x
+  ------
+   0 | pmic_temp
+   1 | batt_v
+   2 | batt_chrg_i
+   3 | batt_dischrg_i
+
+  AXP813
+  ------
+   0 | pmic_temp
+   1 | gpio0_v
+   2 | batt_v
+   3 | batt_chrg_i
+   4 | batt_dischrg_i
+
+
+properties:
+  compatible:
+    enum:
+      - x-powers,axp209-adc
+      - x-powers,axp221-adc
+      - x-powers,axp813-adc
+
+  "#io-channel-cells":
+    const: 1
+
+additionalProperties: false
+
+examples:
+  - |
+    axp221 {
+        adc {
+            compatible = "x-powers,axp221-adc";
+            #io-channel-cells = <1>;
+        };
+    };
+...