At the point smmu_find_add_as() gets called, the bus number might
not be computed. Let's change the name of IOMMU memory region and
just use the devfn and an incrementing index.

The name only is used for debug.
Signed-off-by: NEric Auger <eric.auger@redhat.com>
Message-id: 20180921070138.10114-2-eric.auger@redhat.com
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
[PMM: changed 'uint' to 'unsigned int']
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>