vdpa: Add set/get_vq_affinity callbacks in vdpa_config_ops

This introduces set/get_vq_affinity callbacks in
vdpa_config_ops to support virtqueue affinity
management for vdpa device drivers.

Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20230323053043.35-3-xieyongji@bytedance.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>