systemd: fix PACKAGECONFIG for lz4

systemd: fix PACKAGECONFIG for lz4

Fixed:
MACHINE = "qemux86-64"
PACKAGECONFIG_append_pn-systemd = "lz4"
DISTRO_FEATURES_append = " systemd"
DISTRO_FEATURES_BACKFILL_CONSIDERED += "sysvinit"
VIRTUAL-RUNTIME_init_manager = "systemd"
VIRTUAL-RUNTIME_initscripts = "systemd-compat-units"

$ bitbake core-image-minimal
$ runqemu tmp/deploy/images/qemux86-64/ nographic
/sbin/init: error while loading shared libraries: liblz4.so.1: cannot open shared object file: No such file or directory

Add lz4 to RDEPENDS to fix the problem.

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>