ELOG: Refactor watchdog_tombstone

The symbol watchdog_tombstone is not really about ChromeOS
but ELOG instead. This prepares for furher move of the
watchdog_tombstone implementation.

Change-Id: I8446fa1a395b2d17912a23b87b83277c80828874
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/63300
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>

src/vendorcode/google/chromeos/chromeos.h

@@ -11,6 +11,7 @@
 /* functions implemented in watchdog.c */
 void mark_watchdog_tombstone(void);
 void reboot_from_watchdog(void);
+bool reset_watchdog_tombstone(void);
 #else
 static inline void mark_watchdog_tombstone(void) { return; }
 static inline void reboot_from_watchdog(void) { return; }