doc: Add stitched ciphers to EVP_EncryptInit.pod

These ciphers don't appear to be documented anywhere. Given the
performance[1] benefits I think it makes sense to expose them.

[1] https://software.intel.com/sites/default/files/open-ssl-performance-paper.pdf



Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3067)