global: Convert simple_strtoul() with decimal to dectoul()

It is a pain to have to specify the value 10 in each call. Add a new
dectoul() function and update the code to use it.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/cmd/sound.c b/cmd/sound.c
index fdcde36..f82f2aa 100644
--- a/cmd/sound.c
+++ b/cmd/sound.c
@@ -41,9 +41,9 @@
 	int freq = 400;
 
 	if (argc > 1)
-		msec = simple_strtoul(argv[1], NULL, 10);
+		msec = dectoul(argv[1], NULL);
 	if (argc > 2)
-		freq = simple_strtoul(argv[2], NULL, 10);
+		freq = dectoul(argv[2], NULL);
 
 	ret = uclass_first_device_err(UCLASS_SOUND, &dev);
 	if (!ret)