Bug#866865: Buttons also greyed out with systemd

[donald@trash-mail.com]

I am using Testing/Buster on my bare metal machine with systemd. Since some
days SDDM (now version 0.15.0-1) does also here grey out the shutdown and
reboot buttons. In a VM (with the same OS) the bug does not show.

This may be a race condition bestween the starts of systemd-logind.service
and sddm.service, see https://github.com/sddm/sddm/issues/978 . The
workaround provided there to start sddm after systemd-logind with a
dependency entry works for me.

Chris