exynos: video: Enable stdout env var backward compatibility for LCD

exynos: video: Enable stdout env var backward compatibility for LCD

Commit bb5930d5c97f ("exynos: video: Convert several boards to driver
model for video") converted the Exynos Chromebooks machines to use DM
for video, but this breaks backward compatibility with the stdout env
var since now stdout is expected to be "vidconsole" instead of "lcd".

This causes display to not work when updating u-boot on these boards
if the old stdout env var is used. Since these are consumer devices,
there's no easy way to have a serial console so users may be confused
thinking that u-boot failed to boot, or in the best case will need to
update the stdout env var blindly to make the display to work again.

There's a CONFIG_VIDCONSOLE_AS_LCD config option to workaround this,
so enable it in the Chromebooks' default configuration files to allow
users to change their stdout env var before the workaround is removed.

Suggested-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>