x86/platform/UV: Add basic CPU NMI health check

x86/platform/UV: Add basic CPU NMI health check

Add a low impact health check triggered by the system NMI command
that essentially checks which CPUs are responding to external NMI's.

Signed-off-by: Mike Travis <travis@sgi.com>
Reviewed-by: Russ Anderson <rja@hpe.com>
Reviewed-by: Alex Thorlton <athorlton@sgi.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Dimitri Sivanich <sivanich@hpe.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20170125163517.756690240@asylum.americas.sgi.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>