dt-bindings: watchdog: mediatek: Convert mtk-wdt to json-schema

Convert the MediaTek watchdog bindings to schema.

The original binding only had 4 without a fallback but there is a reset
controller on the "mediatek,mt7986-wdt", "mediatek,mt8186-wdt",
"mediatek,mt8188-wdt" and "mediatek,mt8195-wdt" Since there is no reset
controller for the mt6589, we remove "mediatek,mt6589-wdt" as a
fallback.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Co-developed-by: Allen-KH Cheng <allen-kh.cheng@mediatek.com>
Signed-off-by: Allen-KH Cheng <allen-kh.cheng@mediatek.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Link: https://lore.kernel.org/r/20221101090116.27130-6-allen-kh.cheng@mediatek.com


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