tegra: config: seaboard: Move tegra-common-post to correct place

The NAND defines ended up before this include file, but should be after
it, so it doesn't become a post-pre-NAND.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>