Add ps rules for some doc/ Makefiles.

Add ps rules for some doc/ Makefiles.

* doc/misc/Makefile.in (.texi.dvi): Remove unnecessary suffix rule.

* dos/lispref/Makefile.in (DVIPS): New variable.
(.PHONY): Add ps.
(ps, elisp.ps): New targets.
(clean): Delete ps file.

* doc/lispintro/Makefile.in (.dvi.ps): Remove unnecessary suffix rule.
(.PHONY): Add ps.
(ps, emacs-lisp-intro.ps): New targets.
(clean): Delete ps file.

* doc/emacs/Makefile.in (.texi.dvi): Remove unnecessary suffix rule.
(DVIPS): New variable.
(.PHONY): Add ps.
(ps, emacs.ps, emacs-xtra.ps): New targets.
(clean): Delete ps files.