ARM: tegra: paz00: add support for wakeup gpio key

This adds support for a wakeup gpio which is connected to the
embedded controller. This will be used later on for wakeup from suspend.

Acked-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Marc Dietrich <marvin24@gmx.de>
Signed-off-by: Olof Johansson <olof@lixom.net>