dt-binding: mediatek: mt8192: update mtk-wdt document

update mtk-wdt document for MT8192 platform

Signed-off-by: Crystal Guo <crystal.guo@mediatek.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20201014131936.20584-3-crystal.guo@mediatek.com


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