target/s390x: support SHA-512 extensions

target/s390x: support SHA-512 extensions

In order to fully support MSA_EXT_5, we have to support the SHA-512
special instructions. So implement those.

The implementation began as something TweetNacl-like, and then was
adjusted to be useful here. It's not very beautiful, but it is quite
short and compact, which is what we're going for.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
[ restructure, add missing exception, add comments, fixup CPU model ]
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20220922153820.221811-1-david@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>