Add support in 'perf list' to output tool internal events, currently
only 'duration_time'.

Committer testing:

  $ perf list dur*

  List of pre-defined events (to be used in -e):

    duration_time                                      [Tool event]

  Metric Groups:

  $ perf list sw

  List of pre-defined events (to be used in -e):

    alignment-faults                                   [Software event]
    bpf-output                                         [Software event]
    context-switches OR cs                             [Software event]
    cpu-clock                                          [Software event]
    cpu-migrations OR migrations                       [Software event]
    dummy                                              [Software event]
    emulation-faults                                   [Software event]
    major-faults                                       [Software event]
    minor-faults                                       [Software event]
    page-faults OR faults                              [Software event]
    task-clock                                         [Software event]

    duration_time                                      [Tool event]

  $ perf list | grep duration
    duration_time                                      [Tool event]
         [L1D miss outstandings duration in cycles]
          page walk duration are excluded in Skylake]
          load. EPT page walk duration are excluded in Skylake]
          page walk duration are excluded in Skylake]
          store. EPT page walk duration are excluded in Skylake]
          (instruction fetch) request. EPT page walk duration are excluded in
          instruction fetch request. EPT page walk duration are excluded in
  $
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/r/20190326221823.11518-5-andi@firstfloor.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>