linux: define license

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

linux/linux.mk

@@ -4,6 +4,8 @@
 #
 ###############################################################################
 LINUX_VERSION=$(call qstrip,$(BR2_LINUX_KERNEL_VERSION))
+LINUX_LICENSE = GPLv2
+LINUX_LICENSE_FILES = COPYING
 
 # Compute LINUX_SOURCE and LINUX_SITE from the configuration
 ifeq ($(LINUX_VERSION),custom)