libperf: Move 'idx' from tools/perf to perf_evsel::idx

Move evsel::idx to perf_evsel::idx, so we can move the group interface
to libperf.

Committer notes:

Fixup evsel->idx usage in tools/perf/util/bpf_counter_cgroup.c, that
appeared in my tree in my local tree.

Also fixed up these:

$ find tools/perf/ -name "*.[ch]" | xargs grep 'evsel->idx'
tools/perf/ui/gtk/annotate.c:                      evsel->idx + i);
tools/perf/ui/gtk/annotate.c:                   evsel->idx);
$

That running 'make -C tools/perf build-test' caught.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Requested-by: Shunsuke Nakamura <nakamura.shun@fujitsu.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/20210706151704.73662-3-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/builtin-diff.c b/tools/perf/builtin-diff.c
index f52b3a7..80450c0 100644
--- a/tools/perf/builtin-diff.c
+++ b/tools/perf/builtin-diff.c
@@ -1031,12 +1031,12 @@ static int process_base_stream(struct data__file *data_base,
 			continue;
 
 		es_base = evsel_streams__entry(data_base->evlist_streams,
-					       evsel_base->idx);
+					       evsel_base->core.idx);
 		if (!es_base)
 			return -1;
 
 		es_pair = evsel_streams__entry(data_pair->evlist_streams,
-					       evsel_pair->idx);
+					       evsel_pair->core.idx);
 		if (!es_pair)
 			return -1;