Incorrect initialisation of hardware watchdog

[danielb-tkjcy3rq]

MCUBOOT_WATCHDOG_SETUP() is missing a call to wdt_install_timeout. At least on my hardware (imxrt1170), the unit wasn't rebooting if I deliberately put an infinite loop to run down the watchdog timer.

There is the question of how to get users to set their desired timeout, but I guess that could be solved using a config option?