dt-bindings: iio: dac: add MCP4821

Adds support for MCP48xx series of DACs.

Datasheet: https://ww1.microchip.com/downloads/en/DeviceDoc/22244B.pdf #MCP48x1
Datasheet: https://ww1.microchip.com/downloads/en/DeviceDoc/20002249B.pdf #MCP48x2
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Anshul Dalal <anshulusr@gmail.com>
Link: https://lore.kernel.org/r/20231220151954.154595-1-anshulusr@gmail.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/dac/microchip,mcp4821.yaml

+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/dac/microchip,mcp4821.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Microchip MCP4821 and similar DACs
+
+description: |
+  Supports MCP48x1 (single channel) and MCP48x2 (dual channel) series of DACs.
+  Device supports simplex communication over SPI in Mode 0 and Mode 3.
+
+  +---------+--------------+-------------+
+  | Device  |  Resolution  |   Channels  |
+  |---------|--------------|-------------|
+  | MCP4801 |     8-bit    |      1      |
+  | MCP4802 |     8-bit    |      2      |
+  | MCP4811 |    10-bit    |      1      |
+  | MCP4812 |    10-bit    |      2      |
+  | MCP4821 |    12-bit    |      1      |
+  | MCP4822 |    12-bit    |      2      |
+  +---------+--------------+-------------+
+
+  Datasheet:
+    MCP48x1: https://ww1.microchip.com/downloads/en/DeviceDoc/22244B.pdf
+    MCP48x2: https://ww1.microchip.com/downloads/en/DeviceDoc/20002249B.pdf
+
+maintainers:
+  - Anshul Dalal <anshulusr@gmail.com>
+
+allOf:
+  - $ref: /schemas/spi/spi-peripheral-props.yaml#
+
+properties:
+  compatible:
+    enum:
+      - microchip,mcp4801
+      - microchip,mcp4802
+      - microchip,mcp4811
+      - microchip,mcp4812
+      - microchip,mcp4821
+      - microchip,mcp4822
+
+  reg:
+    maxItems: 1
+
+  vdd-supply: true
+
+  ldac-gpios:
+    description: |
+      Active Low LDAC (Latch DAC Input) pin used to update the DAC output.
+    maxItems: 1
+
+  powerdown-gpios:
+    description: |
+      Active Low SHDN pin used to enter the shutdown mode.
+    maxItems: 1
+
+  spi-cpha: true
+  spi-cpol: true
+
+required:
+  - compatible
+  - reg
+  - vdd-supply
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+
+    spi {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        dac@0 {
+            compatible = "microchip,mcp4821";
+            reg = <0>;
+            vdd-supply = <&vdd_regulator>;
+            ldac-gpios = <&gpio0 1 GPIO_ACTIVE_HIGH>;
+            powerdown-gpios = <&gpio0 2 GPIO_ACTIVE_HIGH>;
+            spi-cpha;
+            spi-cpol;
+        };
+    };