s390x/tcg: Implement VECTOR FP (MAXIMUM|MINIMUM)

For IEEE functions, we can reuse the softfloat implementations. For the
other functions, implement it generically for 32bit/64bit/128bit -
carefully taking care of all weird special cases according to the tables
defined in the PoP.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20210608092337.12221-24-david@redhat.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>