tegra20: enable SPL for tegra20 boards

Add SPL options to tegra20 config files and enable SPL build for
tegra20 boards.  Also remove redundant code from u-boot that is not
contained in SPL.

Signed-off-by: Allen Martin <amartin@nvidia.com>
Acked-by: Stephen Warren <swarren@wwwdotorg.org>
Tested-by: Thierry Reding <thierry.reding@avionic-design.de>
Signed-off-by: Tom Warren <twarren@nvidia.com>
8 files changed