virtio_pci: Use the DMA API if enabled

virtio_pci: Use the DMA API if enabled

This switches to vring_create_virtqueue, simplifying the driver and
adding DMA API support.

This fixes virtio-pci on platforms and busses that have IOMMUs.  This
will break the experimental QEMU Q35 IOMMU support until QEMU is
fixed.  In exchange, it fixes physical virtio hardware as well as
virtio-pci running under Xen.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
(cherry picked from commit 7a5589b240b405d55b2b395554082ec284f414bb)
Orabug: 26388044
Reviewed-by: Khalid Aziz <khalid.aziz@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>