perf callchain: Allow disabling call graphs per event

This patch introduce "call-graph=no" to disable per-event callgraph.

Here is an example.

  perf record -e 'cpu/cpu-cycles,call-graph=fp/,cpu/instructions,call-graph=no/' sleep 1

  perf report --stdio

  # To display the perf.data header info, please use
  --header/--header-only options.
  #
  #
  # Total Lost Samples: 0
  #
  # Samples: 6  of event 'cpu/cpu-cycles,call-graph=fp/'
  # Event count (approx.): 774218
  #
  # Children      Self  Command  Shared Object     Symbol
  # ........  ........  .......  ................  ........................................
  #
    61.94%     0.00%  sleep    [kernel.vmlinux]  [k] entry_SYSCALL_64_fastpath
              |
              ---entry_SYSCALL_64_fastpath
                 |
                 |--97.30%-- __brk
                 |
                  --2.70%-- mmap64
                            _dl_check_map_versions
                            _dl_check_all_versions

    61.94%     0.00%  sleep    [kernel.vmlinux]  [k] perf_event_mmap
              |
              ---perf_event_mmap
                 |
                 |--97.30%-- do_brk
                 |          sys_brk
                 |          entry_SYSCALL_64_fastpath
                 |          __brk
                 |
                  --2.70%-- mmap_region
                            do_mmap_pgoff
                            vm_mmap_pgoff
                            sys_mmap_pgoff
                            sys_mmap
                            entry_SYSCALL_64_fastpath
                            mmap64
                            _dl_check_map_versions
                            _dl_check_all_versions
  ......

  # Samples: 6  of event 'cpu/instructions,call-graph=no/'
  # Event count (approx.): 359692
  #
  # Children      Self  Command  Shared Object     Symbol
  # ........  ........  .......  ................  .................................
  #
     89.03%     0.00%  sleep    [unknown]         [.] 0xffff6598ffff6598
     89.03%     0.00%  sleep    ld-2.17.so        [.] _dl_resolve_conflicts
     89.03%     0.00%  sleep    [kernel.vmlinux]  [k] page_fault

Signed-off-by: Kan Liang <kan.liang@intel.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/1439289050-40510-2-git-send-email-kan.liang@intel.com


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