Print accumulated stat of a hist entry if requested.

To do that, add new HPP_PERCENT_ACC_FNS macro and generate a
perf_hpp_fmt using it.  The __hpp__sort_acc() function sorts entries
by accumulated period value.  When accumulated periods of two entries
are same (i.e. single path callchain) put the caller above since
accumulation tends to put callers on higher position for obvious
reason.

Also add "overhead_children" output field to be selected by user.
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arun Sharma <asharma@fb.com>
Tested-by: Rodrigo Campos <rodrigo@sdfg.com.ar>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Link: http://lkml.kernel.org/r/1401335910-16832-11-git-send-email-namhyung@kernel.orgSigned-off-by: Jiri Olsa <jolsa@kernel.org>