dt-bindings: iio: adc: Add Allwinner D1/T113s/R329/T507 SoCs GPADC

Allwinner's D1/T113s/R329/T507 SoCs have a new general purpose ADC.
This ADC is the same for all of this SoCs. The only difference is
the number of available channels.
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Maksim Kiselev <bigunclemax@gmail.com>
Link: https://lore.kernel.org/r/20230619154252.3951913-4-bigunclemax@gmail.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/adc/allwinner,sun20i-d1-gpadc.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/adc/allwinner,sun20i-d1-gpadc.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Allwinner D1 General Purpose ADC
+
+maintainers:
+  - Maksim Kiselev <bigunclemax@gmail.com>
+
+properties:
+  compatible:
+    enum:
+      - allwinner,sun20i-d1-gpadc
+
+  "#io-channel-cells":
+    const: 1
+
+  "#address-cells":
+    const: 1
+
+  "#size-cells":
+    const: 0
+
+  clocks:
+    maxItems: 1
+
+  interrupts:
+    maxItems: 1
+
+  reg:
+    maxItems: 1
+
+  resets:
+    maxItems: 1
+
+patternProperties:
+  "^channel@[0-9a-f]+$":
+    $ref: adc.yaml
+    type: object
+    description:
+      Represents the internal channels of the ADC.
+
+    properties:
+      reg:
+        items:
+          minimum: 0
+          maximum: 15
+
+    required:
+      - reg
+
+    unevaluatedProperties: false
+
+required:
+  - "#io-channel-cells"
+  - clocks
+  - compatible
+  - interrupts
+  - reg
+  - resets
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/clock/sun20i-d1-ccu.h>
+    #include <dt-bindings/reset/sun20i-d1-ccu.h>
+    #include <dt-bindings/interrupt-controller/irq.h>
+
+    gpadc: adc@2009000 {
+        compatible = "allwinner,sun20i-d1-gpadc";
+        reg = <0x2009000 0x400>;
+        clocks = <&ccu CLK_BUS_GPADC>;
+        resets = <&ccu RST_BUS_GPADC>;
+        interrupts = <73 IRQ_TYPE_LEVEL_HIGH>;
+        #io-channel-cells = <1>;
+
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        channel@0 {
+            reg = <0>;
+        };
+
+        channel@1 {
+            reg = <1>;
+        };
+    };
+...