dt-bindings: ARM: tegra: Document ASUS Transformers

Document Tegra20/30/114-based ASUS Transformer Series tablet devices.
This group includes EeePad TF101, Prime TF201, Pad TF300T, TF300TG
Infinity TF700T, TF701T.

Signed-off-by: David Heidelberg <david@ixit.cz>
Signed-off-by: Anton Bambura <jenneron@protonmail.com>
Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>