sandbox

Add a simple LCD driver which uses SDL to display the image. We update the
image regularly, while still providing for reasonable performance.

Adjust the common lcd code to support sandbox.

For command-line runs we do not want the LCD to be displayed, so add a
--show_lcd option to enable it.

Tested-by: Che-Liang Chiou <clchiou@chromium.org>
Signed-off-by: Simon Glass <sjg@chromium.org>