[coreboot] Watchdog timer (WDT) support on Kabylake w/FSP2.0

[Matt DeVillier]

greetings!  I'm trying to enable WDT support for Kabylake Chromeboxes
(google/fizz) but not having any luck.  The current SoC code doesn't
expose the FSP fields which appear to control this (WdtDisableAndLock,
WatchDog, WatchDogTimerOS, WatchDogTimerBIOS), so I added them to
chip_fsp20.c and set them accordingly in devicetree (though it's
unclear what the values of WatchDogTimerOS/WatchDogTimerBIOS are to
be, the documentation doesn't state if this is a timeout value, units,
etc).  Still, I'm unable to remotely trigger a reset via
/dev/watchdog0.

Has anyone else used this feature, or have any insight as to the
proper FSP settings? AIUI this works properly on older non-FSP
Chromeboxes (Haswell/Broadwell)

cheers,
Matt