dt-bindings: watchdog: Add Loongson-1 watchdog

Add devicetree binding document for Loongson-1 watchdog.
Signed-off-by: Keguang Zhang <keguang.zhang@gmail.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lkml.kernel.org/r/20230511121159.463645-2-keguang.zhang@gmail.comSigned-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

Documentation/devicetree/bindings/watchdog/loongson,ls1x-wdt.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/watchdog/loongson,ls1x-wdt.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Loongson-1 Watchdog Timer
+
+maintainers:
+  - Keguang Zhang <keguang.zhang@gmail.com>
+
+allOf:
+  - $ref: watchdog.yaml#
+
+properties:
+  compatible:
+    enum:
+      - loongson,ls1b-wdt
+      - loongson,ls1c-wdt
+
+  reg:
+    maxItems: 1
+
+  clocks:
+    maxItems: 1
+
+required:
+  - compatible
+  - reg
+  - clocks
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/clock/loongson,ls1x-clk.h>
+    watchdog: watchdog@1fe5c060 {
+        compatible = "loongson,ls1b-wdt";
+        reg = <0x1fe5c060 0xc>;
+
+        clocks = <&clkc LS1X_CLKID_APB>;
+    };