dt-bindings: watchdog: Add Mstar MSC313e WDT devicetree bindings documentation

This adds the documentation for the devicetree bindings of the Mstar
MSC313e watchdog driver, found from MSC313e SoCs and newer.
Signed-off-by: Romain Perier <romain.perier@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210611200801.52139-2-romain.perier@gmail.comSigned-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

Documentation/devicetree/bindings/watchdog/mstar,msc313e-wdt.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/watchdog/mstar,msc313e-wdt.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: MStar Watchdog Device Tree Bindings
+
+maintainers:
+  - Daniel Palmer <daniel@0x0f.com>
+  - Romain Perier <romain.perier@gmail.com>
+
+allOf:
+  - $ref: watchdog.yaml#
+
+properties:
+  compatible:
+    enum:
+      - mstar,msc313e-wdt
+
+  reg:
+    maxItems: 1
+
+  clocks:
+    maxItems: 1
+
+required:
+  - compatible
+  - clocks
+  - reg
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    watchdog@6000 {
+        compatible = "mstar,msc313e-wdt";
+        reg = <0x6000 0x1f>;
+        clocks = <&xtal_div2>;
+    };