s390x/tcg: Implement VECTOR TEST UNDER MASK

s390x/tcg: Implement VECTOR TEST UNDER MASK

Let's return the cc value directly via cpu_env. Unfortunately there
isn't a simple way to calculate the value lazily - one would have to
calculate and store e.g. the population count of the mask and the
result so it can be evaluated in a cc helper.

But as VTM only sets the cc, we can assume the value will be needed soon
either way.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: David Hildenbrand <david@redhat.com>