target/s390x: Check reserved bits of VFMIN/VFMAX's M5

target/s390x: Check reserved bits of VFMIN/VFMAX's M5

VFMIN and VFMAX should raise a specification exceptions when bits 1-3
of M5 are set.

Cc: qemu-stable@nongnu.org
Fixes: da4807527f3b ("s390x/tcg: Implement VECTOR FP (MAXIMUM|MINIMUM)")
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Message-Id: <20230804234621.252522-1-iii@linux.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
(cherry picked from commit 6a2ea6151835aa4f5fee29382a421c13b0e6619f)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>