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/usb/gadget/epautoconf.c b/drivers/usb/gadget/epautoconf.c
index 7da334f..01337d6 100644
--- a/drivers/usb/gadget/epautoconf.c
+++ b/drivers/usb/gadget/epautoconf.c
@@ -144,7 +144,7 @@
 
 	/* report address */
 	if (isdigit(ep->name[2])) {
-		u8	num = simple_strtoul(&ep->name[2], NULL, 10);
+		u8	num = dectoul(&ep->name[2], NULL);
 		desc->bEndpointAddress |= num;
 #ifdef	MANY_ENDPOINTS
 	} else if (desc->bEndpointAddress & USB_DIR_IN) {