CONFIG_WATCHDOG_NOWAYOUT を有効にする

[Ryota Kinukawa]

CONFIG_WATCHDOG_NOWAYOUT とは

If it is set to Y when compiling the kernel, there is no way of disabling the watchdog once it has been started.

ref. https://www.kernel.org/doc/html/latest/watchdog/watchdog-api.html#the-simplest-api

nerves_system_* では有効にするオプション、常にウォッチドッグを有効にしておきたいため