util/perl/OpenSSL/Ordinals.pm: introduce a base version

The idea is that a base version is the minimum version that must be
assigned to all symbols.  The practical result is that, for any new
major release, the version number for all symbols will automatically
be bumped to the new release's version number, if necessary.

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7740)