tegra/iommu: smmu: Use PCI root device

tegra/iommu: smmu: Use PCI root device

Use the PCI root device for finding the SMMU mapping when the
device to be added is a PCI device.

Bug 200076269

Change-Id: Ief853dbc67dcf689e142038a84807e01f86fdcda
Signed-off-by: Alex Waterman <alexw@nvidia.com>
Reviewed-on: http://git-master/r/831981
(cherry picked from commit 12d2dca04e20387d5e4e0216bb1fff8d09df523c)
Reviewed-on: http://git-master/r/934485
Tested-by: Vidya Sagar <vidyas@nvidia.com>
GVS: Gerrit_Virtual_Submit
Reviewed-by: Hayden Du <haydend@nvidia.com>