uboot: add license information

Signed-off-by: Simon Dawson <spdawson@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

boot/uboot/uboot.mk

@@ -6,6 +6,9 @@
 UBOOT_VERSION    = $(call qstrip,$(BR2_TARGET_UBOOT_VERSION))
 UBOOT_BOARD_NAME = $(call qstrip,$(BR2_TARGET_UBOOT_BOARDNAME))
 
+UBOOT_LICENSE = GPLv2+
+UBOOT_LICENSE_FILES = COPYING
+
 UBOOT_INSTALL_IMAGES = YES
 
 ifeq ($(UBOOT_VERSION),custom)