ARM: tegra: Add node for trackpad in Nyan boards

The Nyan boards have a eKTH3000 from Elan as their trackpad, connected
through I2C.

Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Acked-by: Stephen Warren <swarren@nvidia.com>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>