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/bind.c b/cmd/bind.c
index af2f22c..07c629e 100644
--- a/cmd/bind.c
+++ b/cmd/bind.c
@@ -218,13 +218,13 @@
 			return CMD_RET_USAGE;
 		ret = unbind_by_node_path(argv[1]);
 	} else if (!by_node && bind) {
-		int index = (argc > 2) ? simple_strtoul(argv[2], NULL, 10) : 0;
+		int index = (argc > 2) ? dectoul(argv[2], NULL) : 0;
 
 		if (argc != 4)
 			return CMD_RET_USAGE;
 		ret = bind_by_class_index(argv[1], index, argv[3]);
 	} else if (!by_node && !bind) {
-		int index = (argc > 2) ? simple_strtoul(argv[2], NULL, 10) : 0;
+		int index = (argc > 2) ? dectoul(argv[2], NULL) : 0;
 
 		if (argc == 3)
 			ret = unbind_by_class_index(argv[1], index);