ARM: tegra: Add device-tree for ASUS Google Nexus 7

There are few hardware variants of NVIDIA Tegra30-based Nexus 7 device:

1. WiFi-only (named Grouper)
2. GSM (named Tilapia)
3. Using Maxim PMIC (E1565 board ID)
4. Using Ti PMIC (PM269 board ID)

This patch adds device-trees for known and tested variants.

Link: https://wiki.postmarketos.org/wiki/Google_Nexus_7_2012_(asus-grouper)


Tested-by: Pedro Ângelo <pangelo@void.io>
Tested-by: Matt Merhar <mattmerhar@protonmail.com>
Tested-by: Zack Pearsall <zpearsall@yahoo.com>
Signed-off-by: David Heidelberg <david@ixit.cz>
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>