gperf: add license information

Signed-off-by: Simon Dawson <spdawson@gmail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/gperf/gperf.mk

@@ -6,6 +6,8 @@
 
 GPERF_VERSION = 3.0.4
 GPERF_SITE = $(BR2_GNU_MIRROR)/gperf
+GPERF_LICENSE = GPLv3+
+GPERF_LICENSE_FILES = COPYING
 
 $(eval $(autotools-package))
 $(eval $(host-autotools-package))