vDPA/ifcvf: record virtio notify base

This commit records virtio notify base physical addr and
calculate doorbell physical address for vqs.

Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20210602084550.289599-2-lingshan.zhu@intel.com


Signed-off-by: Michael S. Tsirkin <mst@redhat.com>