tegra: video: Merge the display driver into one file

At present we have code in arch/arm and code in drivers/video. Move it all
into drivers/video since it is a display driver and our current approach is
to put all driver code in drivers/.

Make a few functions static now that they are not used outside the file.
Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Anatolij Gustschin <agust@denx.de>
Signed-off-by: Tom Warren <twarren@nvidia.com>