Now hpp formats are linked using perf_hpp_list_node when hierarchy is
enabled.  Use this info to print entries with multiple sort keys in a
single hierarchy properly.

For example, the below example shows using 4 sort keys with 2 levels.

  $ perf report --hierarchy -s '{prev_pid,prev_comm},{next_pid,next_comm}' \
   --percent-limit 1 -i perf.data.sched
  ...
  #    Overhead  prev_pid+prev_comm / next_pid+next_comm
  # ...........  .......................................
  #
      22.36%     0  swapper/0
          9.48%     17773  transmission-gt
          5.25%     109  kworker/0:1H
          1.53%     6524  Xephyr
      21.39%     17773  transmission-gt
          9.52%     0  swapper/0
          9.04%     0  swapper/2
          1.78%     0  swapper/3
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1457361308-514-6-git-send-email-namhyung@kernel.orgSigned-off-by: Ingo Molnar <mingo@kernel.org>