of: Add NVIDIA Tegra memory controller binding

The memory controller on NVIDIA Tegra exposes various knobs that can be
used to tune the behaviour of the clients attached to it.

In addition, the memory controller implements an SMMU (IOMMU) which can
translate I/O virtual addresses to physical addresses for clients. This
is useful for scatter-gather operation on devices that don't support it
natively and for virtualization or process separation.

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