perf ftrace: Detect whether ftrace is enabled on system

To make error messages more accurate, this change detects whether ftrace is
enabled on system by checking trace file "set_ftrace_pid".

Before:

  # perf ftrace
  failed to reset ftrace
  #

After:

  # perf ftrace
  ftrace is not supported on this system
  #

Committer testing:

Doing it in an unprivileged toolbox container on Fedora 40:

Before:

  acme@number:~/git/perf-tools-next$ toolbox enter perf
  ⬢[acme@toolbox perf-tools-next]$ sudo su -
  ⬢[root@toolbox ~]# ~acme/bin/perf ftrace
  failed to reset ftrace
  ⬢[root@toolbox ~]#

After this patch:

  ⬢[root@toolbox ~]# ~acme/bin/perf ftrace
  ftrace is not supported on this system
  ⬢[root@toolbox ~]#

Maybe we could check if we are in such as situation, inside an
unprivileged container, and provide a HINT line?

Reviewed-by: James Clark <[email protected]>
Signed-off-by: Changbin Du <[email protected]>
Tested-by: Arnaldo Carvalho de Melo <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Changbin Du <[email protected]>
Cc: Ian Rogers <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Kan Liang <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

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