perf list: Print all available tool events

Introduce names for the new tool events 'user_time' and 'system_time'.

  $ perf list
  ...
  duration_time                                      [Tool event]
  user_time                                          [Tool event]
  system_time                                        [Tool event]
  ...

Committer testing:

Before:

  $ perf list | grep Tool
  duration_time                                      [Tool event]
  $

After:

  $ perf list | grep Tool
    duration_time                                    [Tool event]
    user_time                                        [Tool event]
    system_time                                      [Tool event]
  $

Signed-off-by: Florian Fischer <florian.fischer@muhq.space>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Xing Zhengjun <zhengjun.xing@linux.intel.com>
Link: http://lore.kernel.org/lkml/20220420174244.1741958-2-florian.fischer@muhq.space
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>