x86/NMI: allow processing unknown NMIs when watchdog is enabled

x86/NMI: allow processing unknown NMIs when watchdog is enabled

Change NMI processing so that if watchdog=force is passed on the
command-line and the NMI is not caused by a perf counter overflow (i.e.
likely not a watchdog "tick"), the NMI is handled by the unknown NMI
handler.

This allows injection of NMIs from IPMI controllers that don't set the
IOCK/SERR bits to trigger the unknown NMI handler rather than be
ignored.

Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Fix command line parsing (don't enable the watchdog on e.g.
"watchdog=xyz").

Signed-off-by: Jan Beulich <jbeulich@suse.com>