arm/tegra: add support for tegra30 based board cardhu

Add support for the tegra30 based cardhu development board. Cardhu is a tablet
formfactor reference design for tegra30. The patch provides a device tree for
the board, updates Makefile.boot to build the dtb, includes the platform in
Kconfig and updates board-dt.c.

Signed-off-by: Peter De Schrijver <pdeschrijver@nvidia.com>
Acked-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Colin Cross <ccross@android.com>
Signed-off-by: Olof Johansson <olof@lixom.net>