arm64: tegra: Add NVIDIA Jetson Nano Developer Kit support

The Jetson Nano Developer Kit is a Tegra X1 based development board. It
is similar to Jetson TX1 but it is not pin compatible. It features 4 GB
of LPDDR4, an SPI NOR flash for early boot firmware and an SD card slot
used for storage.

HDMI 2.0 or DP 1.2 are available for display, four USB ports (3 USB 2.0
and 1 USB 3.0) can be used to attach a variety of peripherals and a PCI
Ethernet controller provides onboard network connectivity. An M.2 Key-E
slot with PCIe x1 adds additional possibilities.

A 40-pin header on the board can be used to extend the capabilities and
exposed interfaces of the Jetson Nano.

Acked-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>