dt-bindings: watchdog: Add compatible for MediaTek MT8186

Add dt-binding documentation of watchdog for MediaTek MT8186 SoC.

Signed-off-by: Rex-BC Chen <rex-bc.chen@mediatek.com>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20220301054405.25021-2-rex-bc.chen@mediatek.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

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

@@ -16,6 +16,7 @@ Required properties:
 	"mediatek,mt7629-wdt", "mediatek,mt6589-wdt": for MT7629
 	"mediatek,mt7986-wdt", "mediatek,mt6589-wdt": for MT7986
 	"mediatek,mt8183-wdt": for MT8183
+	"mediatek,mt8186-wdt", "mediatek,mt6589-wdt": for MT8186
 	"mediatek,mt8516-wdt", "mediatek,mt6589-wdt": for MT8516
 	"mediatek,mt8192-wdt": for MT8192
 	"mediatek,mt8195-wdt", "mediatek,mt6589-wdt": for MT8195