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/lib/fdtdec.c b/lib/fdtdec.c
index 4b097fb..07c7ebe 100644
--- a/lib/fdtdec.c
+++ b/lib/fdtdec.c
@@ -405,7 +405,7 @@
 			continue;
 
 		/* Get the alias number */
-		number = simple_strtoul(path + name_len, NULL, 10);
+		number = dectoul(path + name_len, NULL);
 		if (number < 0 || number >= maxcount) {
 			debug("%s: warning: alias '%s' is out of range\n",
 			      __func__, path);