perf tools: Add reference counting for thread_map object

Adding reference counting for thread_map object, so it could be easily
shared among other objects.

Using thread_map__put instead thread_map__delete and making
thread_map__delete static.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1435012588-9007-5-git-send-email-jolsa@kernel.org
[ Adjustments to move it ahead of the "comm" patches ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/openat-syscall.c

@@ -56,6 +56,6 @@ out_close_fd:
 out_evsel_delete:
 	perf_evsel__delete(evsel);
 out_thread_map_delete:
-	thread_map__delete(threads);
+	thread_map__put(threads);
 	return err;
 }