tegra: add Colibri T20 board support

This adds board support for the Toradex Colibri T20 module.

Working functions:
- SD card boot
- USB boot
- Network
- NAND environment

Signed-off-by: Lucas Stach <dev@lynxeye.de>
Signed-off-by: Tom Warren <twarren@nvidia.com>
8 files changed