ARM: tegra: Enable IOMMU for display controllers on Tegra124

Add iommus properties to the device tree nodes for the two display
controllers found on Tegra124. This will allow the display controllers
to map physically non-contiguous buffers to I/O virtual contiguous
address spaces so that they can be used for scan-out.

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