drivers: watchdog: Make WDT_DISABLE_AT_BOOT default to y
drivers: watchdog: Make WDT_DISABLE_AT_BOOT default to y

This commit consolidates the meaning of WDT_DISABLE_AT_BOOT option as
"disabling watchdog at Zephyr system startup for the SoCs that enable
the watchdog by default after reset", and makes this default to y in
order to prevent unintentional processor reset by the watchdog when
not explicitly configured and fed by the application.

Signed-off-by: Stephanos Ioannidis <dc76e9f0c0006e8f919e0c515c66dbba3982f785@stephanos.io>

galak/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr,finikorg/zephyr,Vudentz/zephyr,Vudentz/zephyr,finikorg/zephyr,Vudentz/zephyr,galak/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,nashif/zephyr,Vudentz/zephyr,galak/zephyr