Story: 2003389
Task: 26436
new systemd depends on lz4. And systemd is included in squashfs, so need to add lz4 to squashfs also.
Removed rpms and rt kernel from the image, since they are not used.
Change-Id: Ic0d8be91b747369bb9a068f41e7c4785d29f8881
Signed-off-by: slin14 <shuicheng.lin@intel.com>