dt-bindings: watchdog: Add compatible for MediaTek MT8188

Add dt-binding documentation of watchdog for MediaTek MT8188 Soc

Signed-off-by: Runyang Chen <runyang.chen@mediatek.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20221026063327.20037-2-Runyang.Chen@mediatek.com


Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>