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>

lib/net_utils.c

@@ -23,7 +23,7 @@ struct in_addr string_to_ip(const char *s)
 		return addr;
 
 	for (addr.s_addr = 0, i = 0; i < 4; ++i) {
-		ulong val = s ? simple_strtoul(s, &e, 10) : 0;
+		ulong val = s ? dectoul(s, &e) : 0;
 		if (val > 255) {
 			addr.s_addr = 0;
 			return addr;