net/virtio: use contiguous allocation for DMA memory

net/virtio: use contiguous allocation for DMA memory

All hardware drivers should allocate IOVA-contiguous
memzones for their hardware resources.

Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
Reviewed-by: Venkatesh Srinivas <venkateshs@google.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Tested-by: Santosh Shukla <santosh.shukla@caviumnetworks.com>
Tested-by: Hemant Agrawal <hemant.agrawal@nxp.com>
Tested-by: Gowrishankar Muthukrishnan <gowrishankar.m@linux.vnet.ibm.com>