KVM: s390: do not set intervention requests for GISA interrupts

If GISA is available, we do not have to kick CPUs out of SIE to deliver
interrupts. The hardware can deliver such interrupts while running.

Cc: Michael Mueller <mimu@linux.vnet.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>