systemd: move "machines" symlinks to systemd-container

systemd: move "machines" symlinks to systemd-container

Move symlinks to the machines.target and var-lib-machines.mount units to
the systemd-container package, where the pointed at units are located as
well.

This avoids an implicit dependency of the systemd package on
systemd-container, which prevented the use of systemd without installing
systemd-container.

(From OE-Core rev: ae3c8d938c261c92ecf06e2d09f7e32bc117ceb8)

Signed-off-by: Matthias Schiffer <matthias.schiffer@ew.tq-group.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>