drm/tegra: Simplify IOMMU group selection

All the devices that make up the DRM device are now part of the same
IOMMU group. This simplifies the handling of the IOMMU attachment and
also avoids exhausting the number of IOMMUs available on early Tegra
SoC generations.

Signed-off-by: Thierry Reding <treding@nvidia.com>
6 files changed