regulator: Add binding for Richtek RT5759 DCDC converter

Add bindings for Richtek RT5759 high-performance DCDC converter.
Signed-off-by: ChiYuan Huang <cy_huang@richtek.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/1648294788-11758-2-git-send-email-u0084500@gmail.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/regulator/richtek,rt5759-regulator.yaml

+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/regulator/richtek,rt5759-regulator.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Richtek RT5759 High Performance DCDC Converter
+
+maintainers:
+  - ChiYuan Huang <cy_huang@richtek.com>
+
+description: |
+  The RT5759 is a high-performance, synchronous step-down DC-DC converter that
+  can deliver up to 9A output current from 3V to 6.5V input supply, The output
+  voltage can be programmable with I2C controlled 7-Bit VID.
+
+  Datasheet is available at
+  https://www.richtek.com/assets/product_file/RT5759/DS5759-00.pdf
+
+properties:
+  compatible:
+    enum:
+      - richtek,rt5759
+      - richtek,rt5759a
+
+  reg:
+    maxItems: 1
+
+  regulator-allowed-modes:
+    description: |
+      buck allowed operating mode
+        0: auto mode (PSKIP: pulse skipping)
+        1: force pwm mode
+    items:
+      enum: [0, 1]
+
+  richtek,watchdog-enable:
+    description: enable the external watchdog reset pin listening
+    type: boolean
+
+allOf:
+  - $ref: regulator.yaml#
+
+  - if:
+      properties:
+        compatible:
+          contains:
+            const: richtek,rt5759
+    then:
+      properties:
+        richtek,watchdog-enable: false
+
+required:
+  - compatible
+  - reg
+
+unevaluatedProperties: false
+
+examples:
+  # example 1 for RT5759
+  - |
+    i2c {
+      #address-cells = <1>;
+      #size-cells = <0>;
+
+      regulator@62 {
+        compatible = "richtek,rt5759";
+        reg = <0x62>;
+        regulator-name = "rt5759-buck";
+        regulator-min-microvolt = <600000>;
+        regulator-max-microvolt = <1500000>;
+        regulator-boot-on;
+      };
+    };
+  # example 2 for RT5759A
+  - |
+    i2c {
+      #address-cells = <1>;
+      #size-cells = <0>;
+
+      regulator@62 {
+        compatible = "richtek,rt5759a";
+        reg = <0x62>;
+        regulator-name = "rt5759a-buck";
+        regulator-min-microvolt = <600000>;
+        regulator-max-microvolt = <1725000>;
+        regulator-boot-on;
+        richtek,watchdog-enable;
+      };
+    };