Add more license tags with SPDX identifiers

Note, that licensing stuff is a nightmare: many packages does not clearly
state their licenses, and often multiple source files are simply copied
together - each with different licensing information in the file headers.

I tried hard to ensure, that the license information extracted into the OpenWRT's
makefiles fit the "spirit" of the packages, e.g. such small packages which
come without a dedicated source archive "inherites" the OpenWRT's own license
in my opinion.

However, I can not garantee that I always picked the correct information
and/or did not miss license information.

Signed-off-by: Michael Heimpold <mhei@heimpold.de>

SVN-Revision: 43155

package/boot/kexec-tools/Makefile

@@ -15,6 +15,9 @@ PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.bz2
 PKG_SOURCE_URL:=@KERNEL/linux/utils/kernel/kexec
 PKG_MD5SUM:=05992bc8c0673fc55be7b6d27e48a8db
 
+PKG_LICENSE:=GPL-2.0
+PKG_LICENSE_FILES:=COPYING
+
 PKG_FIXUP:=autoreconf
 
 PKG_CONFIG_DEPENDS := CONFIG_KEXEC_ZLIB