Add support to handle control virtqueue configurations per virtio
specification. The control virtqueue is implemented in software and no
hardware offloading is involved.

Control VQ configuration need task context, therefore all configurations
are handled in a workqueue created for the purpose.

Modifications are made to the memory registration code to allow for
saving a copy of itolb to be used by the control VQ to access the vring.

The max number of data virtqueus supported by the driver has been
updated to 2 since multiqueue is not supported at this stage and we need
to ensure consistency of VQ indices mapping to either data or control
VQ.
Signed-off-by: Eli Cohen <elic@nvidia.com>
Link: https://lore.kernel.org/r/20210823052123.14909-6-elic@nvidia.comSigned-off-by: Michael S. Tsirkin <mst@redhat.com>