perf metrics: Remove the "No_group" metric group

Rather than place metrics without a metric group in "No_group" place
them in a a metric group that is their name. Still allow such metrics
to be selected if "No_group" is passed, this change just impacts perf
list.
Reviewed-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20240403164636.3429091-1-irogers@google.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/metricgroup.c

@@ -455,7 +455,7 @@ static int metricgroup__add_to_mep_groups(const struct pmu_metric *pm,
 	const char *g;
 	char *omg, *mg;
 
-	mg = strdup(pm->metric_group ?: "No_group");
+	mg = strdup(pm->metric_group ?: pm->metric_name);
 	if (!mg)
 		return -ENOMEM;
 	omg = mg;
@@ -466,7 +466,7 @@ static int metricgroup__add_to_mep_groups(const struct pmu_metric *pm,
 		if (strlen(g))
 			me = mep_lookup(groups, g, pm->metric_name);
 		else
-			me = mep_lookup(groups, "No_group", pm->metric_name);
+			me = mep_lookup(groups, pm->metric_name, pm->metric_name);
 
 		if (me) {
 			me->metric_desc = pm->desc;