dt-bindings: tegra: Add Colibri T30 device tree binding documentation

Add the device tree binding documentation for Colibri T30 which was
missing so far.

Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>