perf-report: Add modes for inherited stats and no-samples

Now that we can collect per task statistics, add modes that
make use of that facility.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>