iommu/tegra: gart: Don't use managed resources

GART is a part of the Memory Controller driver that is always built-in,
hence there is no benefit from the use of managed resources.

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