KVM: Recover IRTE to remapped mode if the interrupt is not single-destination

When the interrupt is not single destination any more, we need
to change back IRTE to remapped mode explicitly.

Signed-off-by: Feng Wu <feng.wu@intel.com>
Reviewed-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>