vduse: Support get_vq_affinity callback

This implements get_vq_affinity callback so that
the virtio-blk driver can build the blk-mq queues
based on the irq callback affinity.

Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
Message-Id: <20230323053043.35-7-xieyongji@bytedance.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>