tegra: video: Convert tegra20 LCD driver to driver model

Move this driver over to use driver model. This involves rearranging the
code somewhat. The effect is that everything is run from the probe() method.

Boards which use this are fixed up, but only seaboard is tested.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Anatolij Gustschin <agust@denx.de>
Signed-off-by: Tom Warren <twarren@nvidia.com>