perf hist: Set levels in output_field_add()

perf hist: Set levels in output_field_add()

It turns out that the output fields didn't consider the hierarchy mode
and put all the fields in the same level.  To support hierarchy, each
non-output field should be in a separate level.

Pass a pointer to level to output_field_add() and make it increase the
level when it sees non-output fields.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250331073722.4695-4-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>