Make IV/buf in prov_cipher_ctx_st aligned

Make IV/buf in prov_cipher_ctx_st aligned

Make IV/buf aligned will drastically improve performance
as some architecture performs badly on misaligned memory
access.

Ref to
https://gist.github.com/ZenithalHourlyRate/7b5175734f87acb73d0bbc53391d7140#file-2-openssl-long-md
Ref to
openssl#18197

Signed-off-by: Hongren (Zenithal) Zheng <i@zenithal.me>
Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/18267)

(cherry picked from commit 2787a709c984d3884e1726383c2f2afca428d795)