vduse: switch to use virtio map API instead of DMA API

vduse: switch to use virtio map API instead of DMA API

Lacking the support of device specific mapping supported in virtio,
VDUSE must trick the DMA API in order to make virtio-vdpa transport
work. This is done by advertising vDPA device as dma device with a
VDUSE specific dma_ops even if it doesn't do DMA at all.

This will be fixed by this patch. Thanks to the new mapping operations
support by virtio and vDPA. VDUSE can simply switch to advertise its
specific mappings operations to virtio via virtio-vdpa then DMA API is
not needed for VDUSE any more and iova domain could be used as the
mapping token instead.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20250924070045.10361-3-jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Eugenio Pérez <eperezma@redhat.com>