Ensure that ECX keys pass EVP_PKEY_param_check()

Ensure that ECX keys pass EVP_PKEY_param_check()

RSA keys have no parameters and pass EVP_PKEY_param_check(). Previously,
ECX keys had no parammeters and failed EVP_PKEY_param_check(). We should
be consistent. It makes more sense to always pass, and therefore this
commit implements that behaviour.

Fixes #14482

Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/14485)