s390x/kvm: Fix vector validity bit in device machine checks

Device hotplugs trigger a crw machine check. All machine checks
have validity bits for certain register types. With vector support
we also have to claim that vector registers are valid.
This is a band-aid suitable for stable. Long term we should
create the full  mcic value dynamically depending on the active
features in the kernel interrupt handler.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Cc: qemu-stable@nongnu.org
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>