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/nvedit.c b/cmd/nvedit.c
index 02a99b4..ddc715b 100644
--- a/cmd/nvedit.c
+++ b/cmd/nvedit.c
@@ -423,7 +423,7 @@
 	 * the size.  Otherwise we echo it as part of the
 	 * message.
 	 */
-	i = simple_strtoul(argv[argc - 1], &endptr, 10);
+	i = dectoul(argv[argc - 1], &endptr);
 	if (*endptr != '\0') {			/* no size */
 		size = CONFIG_SYS_CBSIZE - 1;
 	} else {				/* size given */