perf script: Allow showing the --switch-on event

perf script: Allow showing the --switch-on event

One may want to see the --switch-on event as well, allow for that, using
the previous cset example:

  # perf script --switch-on syscalls:sys_enter_nanosleep --show-on-off
        sleep 13638 [001] 108237.582286: syscalls:sys_enter_nanosleep: rqtp: 0x7fff1948ac40, rmtp: 0x00000000
        sleep 13638 [001] 108237.582289:     sched:sched_stat_runtime: comm=sleep pid=13638 runtime=578104 [ns] vruntime=202889459556 [ns]
        sleep 13638 [001] 108237.582291:           sched:sched_switch: sleep:13638 [120] S ==> swapper/1:0 [120]
      swapper     0 [001] 108238.582428:           sched:sched_waking: comm=sleep pid=13638 prio=120 target_cpu=001
      swapper     0 [001] 108238.582458:           sched:sched_wakeup: sleep:13638 [120] success=1 CPU:001
        sleep 13638 [001] 108238.582698:     sched:sched_stat_runtime: comm=sleep pid=13638 runtime=173915 [ns] vruntime=202889633471 [ns]
        sleep 13638 [001] 108238.582782:     sched:sched_process_exit: comm=sleep pid=13638 prio=120
  #
  # perf script --switch-on syscalls:sys_enter_nanosleep
        sleep 13638 [001] 108237.582289:     sched:sched_stat_runtime: comm=sleep pid=13638 runtime=578104 [ns] vruntime=202889459556 [ns]
        sleep 13638 [001] 108237.582291:           sched:sched_switch: sleep:13638 [120] S ==> swapper/1:0 [120]
      swapper     0 [001] 108238.582428:           sched:sched_waking: comm=sleep pid=13638 prio=120 target_cpu=001
      swapper     0 [001] 108238.582458:           sched:sched_wakeup: sleep:13638 [120] success=1 CPU:001
        sleep 13638 [001] 108238.582698:     sched:sched_stat_runtime: comm=sleep pid=13638 runtime=173915 [ns] vruntime=202889633471 [ns]
        sleep 13638 [001] 108238.582782:     sched:sched_process_exit: comm=sleep pid=13638 prio=120
  #

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: William Cohen <wcohen@redhat.com>
Cc: Florian Weimer <fweimer@redhat.com>
Link: https://lkml.kernel.org/n/tip-0omwwoywj1v63gu8cz0tr0cy@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>