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/gpio/mxs_gpio.c b/drivers/gpio/mxs_gpio.c
index 5775a22..7b9d88a 100644
--- a/drivers/gpio/mxs_gpio.c
+++ b/drivers/gpio/mxs_gpio.c
@@ -123,12 +123,12 @@
 	unsigned bank, pin;
 	char *end;
 
-	bank = simple_strtoul(name, &end, 10);
+	bank = dectoul(name, &end);
 
 	if (!*end || *end != ':')
 		return bank;
 
-	pin = simple_strtoul(end + 1, NULL, 10);
+	pin = dectoul(end + 1, NULL);
 
 	return (bank << MXS_PAD_BANK_SHIFT) | (pin << MXS_PAD_PIN_SHIFT);
 }