tests/tcg: drop -cpu max from s390x sha512-mvx invocation

tests/tcg: drop -cpu max from s390x sha512-mvx invocation

With -cpu max we get a warning:

  qemu-s390x: warning: 'msa5-base' requires 'kimd-sha-512'.

But dropping the -cpu max and it still runs fine.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20220309112248.4083619-1-alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Tested-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>