ARM: tegra: Enable Venice2 keyboard

The keyboard on Venice2 is attached to the ChromeOS embedded controller.
Add the corresponding device tree nodes and use the MATRIX_KEY define to
encode keycodes.

Signed-off-by: Rhyland Klein <rklein@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>