vfio/container: Discover IOMMU type before creating the container

vfio/container: Discover IOMMU type before creating the container

Since the QEMU struct type representing the VFIO container is deduced
from the IOMMU type exposed by the host, this type should be well
defined *before* creating the container struct. This will be necessary
to instantiate a QOM object of the correct type in future changes.

Rework vfio_set_iommu() to extract the part doing the container
initialization and move it under vfio_create_container().

Reviewed-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Tested-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Cédric Le Goater <clg@redhat.com>