perf stat: Only print NMI watchdog hint when enabled

Only print the NMI watchdog hint when that watchdog it actually enabled.

This avoids printing these unnecessarily.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/n/tip-lnw7edxnqsphkmeew857wz1i@git.kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>