vDPA/ifcvf: retire ifcvf_start_datapath and ifcvf_add_status

Rather than former lazy-initialization mechanism,
now the virtqueue operations and driver_features related
ops access the virtio registers directly to take
immediate actions. So ifcvf_start_datapath() should
retire.

ifcvf_add_status() is retierd because we should not change
device status by a vendor driver's decision, this driver should
only set device status which is from virito drivers
upon vdpa_ops.set_status()

Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20230526145254.39537-4-lingshan.zhu@intel.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>