kbuild: Add make tarxz-pkg build option

Signed-off-by: Zdenek Kaspar <zkaspar82@gmail.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>
diff --git a/scripts/package/buildtar b/scripts/package/buildtar
index 51b2aa0..83c9c04 100644
--- a/scripts/package/buildtar
+++ b/scripts/package/buildtar
@@ -35,6 +35,10 @@
 		compress="bzip2 -c9"
 		file_ext=".bz2"
 		;;
+	tarxz-pkg)
+		compress="xz -c9"
+		file_ext=".xz"
+		;;
 	*)
 		echo "Unknown tarball target \"${1}\" requested, please add it to ${0}." >&2
 		exit 1