Add missing macros for DHxparams
Add missing macros for DHxparams

DHparams has d2i_DHparams_fp, d2i_DHxparams_bio etc, but the equivalent
macros for DHxparams were omitted.

Reviewed-by: Rich Salz <c04971a99e5a9ee80eaab4b1deb37e845b0bd697@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3111)
openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl