arm64: tegra: Add support for NVIDIA Shield TV

Add initial device-tree support for NVIDIA Shield TV (a.k.a. Darcy)
based upon Tegra210 SoC with 3 GiB of LPDDR4 RAM.

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