dt-bindings: watchdog: migrate mt7621 text bindings to YAML

Soc Mt7621 Watchdog bindings used text format, so migrate them to YAML.
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20220926162549.805108-1-sergio.paracuellos@gmail.comSigned-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

Documentation/devicetree/bindings/watchdog/mediatek,mt7621-wdt.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/watchdog/mediatek,mt7621-wdt.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Ralink Watchdog Timers
+
+maintainers:
+  - Sergio Paracuellos <sergio.paracuellos@gmail.com>
+
+allOf:
+  - $ref: watchdog.yaml#
+
+properties:
+  compatible:
+    const: mediatek,mt7621-wdt
+
+  reg:
+    maxItems: 1
+
+required:
+  - compatible
+  - reg
+
+additionalProperties: false
+
+examples:
+  - |
+    watchdog@100 {
+      compatible = "mediatek,mt7621-wdt";
+      reg = <0x100 0x100>;
+    };

Documentation/devicetree/bindings/watchdog/mt7621-wdt.txt

-Ralink Watchdog Timers
-
-Required properties:
-- compatible: must be "mediatek,mt7621-wdt"
-- reg: physical base address of the controller and length of the register range
-
-Example:
-
-	watchdog@100 {
-		compatible = "mediatek,mt7621-wdt";
-		reg = <0x100 0x10>;
-	};