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>

README

@@ -1642,14 +1642,6 @@ CBFS (Coreboot Filesystem) support
 			=> vertically centered image
 			   at x = dspWidth - bmpWidth - 9
 
-		CONFIG_SPLASH_SCREEN_PREPARE
-
-		If this option is set then the board_splash_screen_prepare()
-		function, which must be defined in your code, is called as part
-		of the splash screen display sequence. It gives the board an
-		opportunity to prepare the splash image data before it is
-		processed and sent to the frame buffer by U-Boot.
-
 - Gzip compressed BMP image support: CONFIG_VIDEO_BMP_GZIP
 
 		If this option is set, additionally to standard BMP

common/splash.c

@@ -21,16 +21,11 @@
  */
 
 #include <splash.h>
-#include <config.h>
 
-#ifdef CONFIG_SPLASH_SCREEN_PREPARE
-int splash_screen_prepare(void)
-{
-	return board_splash_screen_prepare();
-}
-#else
-int splash_screen_prepare(void)
+int __splash_screen_prepare(void)
 {
 	return 0;
 }
-#endif
+
+int splash_screen_prepare(void)
+	__attribute__ ((weak, alias("__splash_screen_prepare")));

doc/README.splashprepare

+---------------------------------------------------------------------
+Splash Screen
+---------------------------------------------------------------------
+The splash_screen_prepare() function is a weak function defined in
+common/splash.c. It is called as part of the splash screen display
+sequence. It gives the board an opportunity to prepare the splash
+image data before it is processed and sent to the frame buffer by
+U-Boot.  Define your own version to use this feature.