Document and add macros for additional DSA options

EVP_PKEY_CTRL_DSA_PARAMGEN_Q_BITS and EVP_PKEY_CTRL_DSA_PARAMGEN_MD are only
exposed from EVP_PKEY_CTX_ctrl, which means callers must write more error-prone
code (see also issue #1319). Add the missing wrapper macros and document them.

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/8093)