dm: led: Add a driver for GPIO-controlled LEDs

Add a simple driver which allows use of LEDs attached to GPIOs. The linux
device tree binding is used.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/led/Makefile b/drivers/led/Makefile
index b39b205..990129e 100644
--- a/drivers/led/Makefile
+++ b/drivers/led/Makefile
@@ -6,3 +6,4 @@
 #
 
 obj-$(CONFIG_LED) += led-uclass.o
+obj-$(CONFIG_LED_GPIO) += led_gpio.o