memory: Add IOMMU_NOTIFIER_DEVIOTLB_UNMAP IOMMUTLBNotificationType

This allows us to differentiate between regular IOMMU map/unmap events
and DEVIOTLB unmap. Doing so, notifiers that only need device IOTLB
invalidations will not receive regular IOMMU unmappings.

Adapt intel and vhost to use it.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20201116165506.31315-4-eperezma@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>