dt-bindings: hwmon: Add Sophgo SG2042 external hardware monitor support

Due to the design, Sophgo SG2042 use an external MCU to provide
hardware information, thermal information and reset control.

Add bindings for this monitor device.

Signed-off-by: Inochi Amaoto <inochiama@outlook.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Tested-by: Chen Wang <unicorn_wang@outlook.com>
Reviewed-by: Chen Wang <unicorn_wang@outlook.com>
Message-ID: <IA1PR20MB49538276F283C4D01364AEB6BB822@IA1PR20MB4953.namprd20.prod.outlook.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Documentation/devicetree/bindings/hwmon/sophgo,sg2042-hwmon-mcu.yaml

@@ -0,0 +1,43 @@
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/hwmon/sophgo,sg2042-hwmon-mcu.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Sophgo SG2042 onboard MCU support
+
+maintainers:
+  - Inochi Amaoto <inochiama@outlook.com>
+
+properties:
+  compatible:
+    const: sophgo,sg2042-hwmon-mcu
+
+  reg:
+    maxItems: 1
+
+  "#thermal-sensor-cells":
+    const: 1
+
+required:
+  - compatible
+  - reg
+  - "#thermal-sensor-cells"
+
+allOf:
+  - $ref: /schemas/thermal/thermal-sensor.yaml#
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    i2c {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        hwmon@17 {
+            compatible = "sophgo,sg2042-hwmon-mcu";
+            reg = <0x17>;
+            #thermal-sensor-cells = <1>;
+        };
+    };