arm64: tegra: Add Tegra194 chip device tree

Add the chip-level device tree, including binding headers, for the
NVIDIA Tegra194 "Xavier" system-on-chip. Only a small subset of devices
are initially available, enough to boot to UART console.

Signed-off-by: Mikko Perttunen <mperttunen@nvidia.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>