Add a new aw_bits attribute to the iommu device to control
the address width of the intel-iommu

Signed-off-by Menno Lageman <menno.lageman@oracle.com>
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
Reviewed-by: NMichal Privoznik <mprivozn@redhat.com>