[packages] xz: add new package

git-svn-id: svn://svn.openwrt.org/openwrt@36316 3c298f89-4303-0410-b956-a3cf2f4a3e73
[packages] squashfs-tools: modularize package

git-svn-id: svn://svn.openwrt.org/openwrt@36317 3c298f89-4303-0410-b956-a3cf2f4a3e73