perf tools: Add unit_number__scnprintf function

Add unit_number__scnprintf function to display size units and use it in
-m option info message.

Before:
  $ perf record -m 10M ls
  rounding mmap pages size to 16777216 bytes (4096 pages)
  ...

After:
  $ perf record -m 10M ls
  rounding mmap pages size to 16M (4096 pages)
  ...

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1483955520-29063-2-git-send-email-jolsa@kernel.org
[ Rename it to unit_number__scnprintf for consistency ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/builtin-test.c

@@ -246,6 +246,10 @@ static struct test generic_tests[] = {
 			.get_desc	= test__clang_subtest_get_desc,
 		}
 	},
+	{
+		.desc = "unit_number__scnprintf",
+		.func = test__unit_number__scnprint,
+	},
 	{
 		.func = NULL,
 	},