main/postmarketos-ui-*: depend on polkit-libs-elogind

Fix for having polkit-libs getting pulled in instead of polkit-libs-elogind and thereby breaking pkexec (issue 1181).

should fix #1181 (closed), but I didn't have time to test it.

@MartijnBraam:

• can you verify that this works as intended?
• backport this to v21.06?