emacs: Only set one variable per setq form

It's a bit weird to avoid having to write the "(setq ... )" more than
once, just because we can.  In a language that uses '=' for the same
purpose we also happily use that once per assignment.

While there are no benefit to using just one 'setq' there are some
drawbacks.  It is not always clear on first what is a key and what a
value and as a result it is easy to make a mistake.  Also it becomes
harder to comment out just one assignment.