s390x assembly pack: allow alignment hints for vector load/store

z14 introduced alignment hints to help vector load/store
performance. For its predecessors, alignment hint defaults
to 0 (no alignment indicated).

Signed-off-by: Patrick Steuer <patrick.steuer@de.ibm.com>

Reviewed-by: Paul Dale <paul.dale@oracle.com>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/8181)