util/mkdef.pl: prepare for DEPRECATEDIN_X

This is in preparation for new versioning scheme, where the
recommendation is to start deprecations at major version boundary.

Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7724)