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/board/synopsys/hsdk/env-lib.c b/board/synopsys/hsdk/env-lib.c
index e225838..fd54ac7 100644
--- a/board/synopsys/hsdk/env-lib.c
+++ b/board/synopsys/hsdk/env-lib.c
@@ -254,7 +254,7 @@
 	if (map[i].type == ENV_HEX)
 		map[i].val->val = hextoul(argv[1], &endp);
 	else
-		map[i].val->val = simple_strtoul(argv[1], &endp, 10);
+		map[i].val->val = dectoul(argv[1], &endp);
 
 	map[i].val->set = true;