dm: Add support for LEDs

Add a simple uclass for LEDs, so that these can be controlled by the device
tree and activated when needed. LEDs are referred to by their label.

This implementation requires a driver for each type of LED (e.g GPIO, I2C).

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/scripts/Makefile.spl b/scripts/Makefile.spl
index bcc7ca2..6b32618 100644
--- a/scripts/Makefile.spl
+++ b/scripts/Makefile.spl
@@ -64,6 +64,7 @@
 libs-$(CONFIG_SPL_SPI_FLASH_SUPPORT) += drivers/mtd/spi/
 libs-$(CONFIG_SPL_SPI_SUPPORT) += drivers/spi/
 libs-y += fs/
+libs-$(CONFIG_SPL_LED_SUPPORT) += drivers/led/
 libs-$(CONFIG_SPL_LIBGENERIC_SUPPORT) += lib/
 libs-$(CONFIG_SPL_POWER_SUPPORT) += drivers/power/ drivers/power/pmic/
 libs-$(CONFIG_SPL_MTD_SUPPORT) += drivers/mtd/