vhost-vdpa: passing iotlb to IOMMU mapping helpers

To prepare for the ASID support for vhost-vdpa, try to pass IOTLB
object to dma helpers. No functional changes, it's just a preparation
for support multiple IOTLBs.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Gautam Dawar <gdawar@xilinx.com>
Message-Id: <20220330180436.24644-4-gdawar@xilinx.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>