libp11: add PKG_LICENSE information

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

libs/libp11/Makefile

@@ -11,6 +11,8 @@ PKG_NAME:=libp11
 PKG_VERSION:=20131021
 PKG_RELEASE:=1
 PKG_MAINTAINER:=Daniel Golle <daniel@makrotopia.org>
+PKG_LICENSE:=LGPL-2.1+
+PKG_LICENSE_FILES:=COPYING
 
 PKG_RELEASE=$(PKG_SOURCE_VERSION)