Comment # 3 on bug 1228759 from Takashi Iwai

As far as I see, kernel-default has only Requires: suse-module-tools, and
suse-module-tools is the one that actually calls sdboot stuff.
So, if any, we should add the dependency to suse-module-tools.spec.

The movement from post to posttrans had some issues in the past.  I guess it'd
be saner to put the proper dependencies.  So I would go for adding

Requires: (systemd-boot if systemd-boot)

to suse-module-tools.spec.