perf ui/stdio: Implement hierarchy output mode

The hierarchy output mode is to group entries for each level so that
user can see higher level picture more easily.  It also helps to find
out which component is most costly.  The output will look like below:

      15.11%     swapper
         14.97%     [kernel.vmlinux]
          0.09%     [libahci]
          0.05%     [iwlwifi]
      10.29%     irq/33-iwlwifi
          6.45%     [kernel.vmlinux]
          1.41%     [mac80211]
          1.15%     [iwldvm]
          1.14%     [iwlwifi]
          0.14%     [cfg80211]
       4.81%     firefox
          3.92%     libxul.so
          0.34%     [kernel.vmlinux]

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Pekka Enberg <penberg@kernel.org>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1456326830-30456-10-git-send-email-namhyung@kernel.org


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