perf stat: Don't display metric header for non-leader uncore events

On an Intel tigerlake laptop a metric like:

    {
        "BriefDescription": "Test",
        "MetricExpr": "imc_free_running@data_read@ + imc_free_running@data_write@",
        "MetricGroup": "Test",
        "MetricName": "Test",
        "ScaleUnit": "6.103515625e-5MiB"
    },

Will have 4 events:

  uncore_imc_free_running_0/data_read/
  uncore_imc_free_running_0/data_write/
  uncore_imc_free_running_1/data_read/
  uncore_imc_free_running_1/data_write/

If aggregration is disabled with metric-only 2 column headers are
needed:

  $ perf stat -M test --metric-only -A -a sleep 1

   Performance counter stats for 'system wide':

                    MiB  Test            MiB  Test
  CPU0                 1821.0               1820.5

But when not, the counts aggregated in the metric leader and only 1
column should be shown:

  $ perf stat -M test --metric-only -a sleep 1
   Performance counter stats for 'system wide':

              MiB  Test
                5909.4

         1.001258915 seconds time elapsed

Achieve this by skipping events that aren't metric leaders when
printing column headers and aggregation isn't disabled.

The bug is long standing, the fixes tag is set to a refactor as that
is as far back as is reasonable to backport.

Fixes: 088519f ("perf stat: Move the display functions to stat-display.c")
Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kaige Ye <ye@kaige.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: K Prateek Nayak <kprateek.nayak@amd.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Yicong Yang <yangyicong@hisilicon.com>
Link: https://lore.kernel.org/r/20240510051309.2452468-1-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/stat-display.c

@@ -1223,6 +1223,9 @@ static void print_metric_headers(struct perf_stat_config *config,
 
 	/* Print metrics headers only */
 	evlist__for_each_entry(evlist, counter) {
+		if (config->aggr_mode != AGGR_NONE && counter->metric_leader != counter)
+			continue;
+
 		os.evsel = counter;
 
 		perf_stat__print_shadow_stats(config, counter, 0,