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/drivers/gpio/gpio-uclass.c b/drivers/gpio/gpio-uclass.c
index 131099c..8c77777 100644
--- a/drivers/gpio/gpio-uclass.c
+++ b/drivers/gpio/gpio-uclass.c
@@ -122,7 +122,7 @@
 	int numeric;
 	int ret;
 
-	numeric = isdigit(*name) ? simple_strtoul(name, NULL, 10) : -1;
+	numeric = isdigit(*name) ? dectoul(name, NULL) : -1;
 	for (ret = uclass_first_device(UCLASS_GPIO, &dev);
 	     dev;
 	     ret = uclass_next_device(&dev)) {