ARM: tegra: Add memory controller support for Tegra30

Collapses the old memory-controller and IOMMU device tree nodes into a
single node to more accurately describe the hardware.

While this is an incompatible change there are no users of the IOMMU on
Tegra, even though a driver has existed for some time.

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