Input: tegra-kbc - add device tree bindings

This adds a simple device tree binding to the tegra keyboard controller.

Also, mark the default keymap as __devinitdata since it is not referenced
after boot.

Signed-off-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>