iommu/tegra: Add support for struct iommu_device

Add a struct iommu_device to each tegra-smmu and register it
with the iommu-core. Also link devices added to the driver
to their respective hardware iommus.

Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>