Fix d2i_ECPKParameters_fp and i2d_ECPKParameters_fp macros

Fix d2i_ECPKParameters_fp and i2d_ECPKParameters_fp macros

These functions are part of the public API but we don't have tests
covering their usage.
They are actually implemented as macros and the absence of tests has
caused them to fall out-of-sync with the latest changes to ASN1 related
functions and cause compilation warnings.

This commit fixes the public headers to reflect these changes.

Fixes #12443

Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/16355)