ARM: dts: tegra: enable NAND flash on Colibri T20

This enables the on-module ONFI conformant NAND flash.

Signed-off-by: Lucas Stach <dev@lynxeye.de>
Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Thierry Reding <treding@nvidia.com>