video: lcd: Make splash_screen_prepare weak, remove config macro

Remove CONFIG_SPLASH_SCREEN_PREPARE from README
Add doc/README.splashprepare to document functionality

Signed-off-by: Robert Winkler <robert.winkler@boundarydevices.com>
Acked-by: Igor Grinberg <grinberg@compulab.co.il>
3 files changed