bus/vdev: add driver IOVA VA mode requirement

bus/vdev: add driver IOVA VA mode requirement

This patch adds driver flag in vdev bus driver so that
vdev drivers can require VA IOVA mode to be used, which
for example the case of Virtio-user PMD.

The patch implements the .get_iommu_class() callback, that
is called before devices probing to determine the IOVA mode
to be used, and adds a check right before the device is
probed to ensure compatible IOVA mode has been selected.

It also adds a ABI exception rule to accommodate with an
update on the driver registration API

Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Acked-by: David Marchand <david.marchand@redhat.com>
Reviewed-by: Chenbo Xia <chenbo.xia@intel.com>