target: enable XZ BCJ decompressor code after r35097

Required to actually be able to mount squashfs xz compressed
filesystems.

Signed-off-by: Florian Fainelli <florian@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@35156 3c298f89-4303-0410-b956-a3cf2f4a3e73