ARM: tegra: seaboard: enable keyboard in DT

Enable Tegra based keyboard controller and populate the key matrix for
seaboard. The key matrix was originally on driver code which is removed
to have clean driver. The key mapping is now passed through dts file.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>