Useful for getting stack traces for hardware events not handled by
PERF_TYPE_HARDWARE.

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tom Zanussi <tzanussi@gmail.com>
Signed-off-by: Arun Sharma <asharma@fb.com>
Link: http://lkml.kernel.org/n/tip-qimdcdpekjqxuyqovy4kjusx@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>