dm: gpio: Add dm_gpio_request() to manually request a GPIO

This function can be used for testing to manually request a GPIO for use,
without resorting to the legacy GPIO API.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/gpio/gpio-uclass.c b/drivers/gpio/gpio-uclass.c
index c6fd580..4efda31 100644
--- a/drivers/gpio/gpio-uclass.c
+++ b/drivers/gpio/gpio-uclass.c
@@ -127,7 +127,7 @@
 	return ops->xlate ? ops->xlate(desc->dev, desc, args) : 0;
 }
 
-static int dm_gpio_request(struct gpio_desc *desc, const char *label)
+int dm_gpio_request(struct gpio_desc *desc, const char *label)
 {
 	struct udevice *dev = desc->dev;
 	struct gpio_dev_priv *uc_priv;