DOCS: Add translation information for EVP_MD_CTX_ctrl()

DOCS: Add translation information for EVP_MD_CTX_ctrl()

EVP_MD_CTX_ctrl() translates some known control commands when faced
with a fetched EVP_MD, so we need to document it.

This also ensures that we don't drop the information on the "micalg"
parameter entirely.

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/11270)