perf map: Move comparision of map's dso_id to a separate function

We'll use it when doing DSO lookups using dso_ids.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-u2nr1oq03o0i29w2ay9jx03s@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/map.h

@@ -28,6 +28,8 @@ struct dso_id {
 	u64	ino_generation;
 };
 
+int dso_id__cmp(struct dso_id *a, struct dso_id *b);
+
 struct map {
 	union {
 		struct rb_node	rb_node;