dt-bindings: hwmon: add missing tmp421 binding

Add basic description of the tmp421 driver DT bindings.

Signed-off-by: Krzysztof Adamski <krzysztof.adamski@nokia.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/84ac871e30a406a1613d140a084b4f3390753099.1634206677.git.krzysztof.adamski@nokia.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Documentation/devicetree/bindings/hwmon/ti,tmp421.yaml

@@ -0,0 +1,43 @@
+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/hwmon/ti,tmp421.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: TMP42x/TMP44x temperature sensor
+
+maintainers:
+  - Guenter Roeck <linux@roeck-us.net>
+
+description: |
+  ±1°C Remote and Local temperature sensor
+  https://www.ti.com/lit/ds/symlink/tmp422.pdf
+
+properties:
+  compatible:
+    enum:
+      - ti,tmp421
+      - ti,tmp422
+      - ti,tmp423
+      - ti,tmp441
+      - ti,tmp442
+  reg:
+    maxItems: 1
+
+required:
+  - compatible
+  - reg
+
+additionalProperties: false
+
+examples:
+  - |
+    i2c {
+      #address-cells = <1>;
+      #size-cells = <0>;
+
+      sensor@4c {
+        compatible = "ti,tmp422";
+        reg = <0x4c>;
+      };
+    };