A set of watchdog/softlockup related improvements:

 - Enforce that the watchdog timestamp is always valid on boot. The
   original implementation caused a watchdog disabled gap of one second in
   the boot process due to truncation of the underlying sched clock. The
   sched clock is divided by 1e9 to convert nanoseconds to seconds. So for
   the first second of the boot process the result is 0 which is at the
   same time the indicator to disable the watchdog. The trivial fix is to
   change the disabled indicator to ULONG_MAX.

 - Two cleanup patches removing unused and redundant code which got
   forgotten to be cleaned up in previous changes.
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