Convert CONFIG_SPLASH_SCREEN et al to Kconfig

This converts the following to Kconfig:
   CONFIG_SPLASH_SCREEN
   CONFIG_SPLASH_SCREEN_ALIGN
   CONFIG_SPLASHIMAGE_GUARD
   CONFIG_SPLASH_SOURCE

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/mx6sabreauto_defconfig b/configs/mx6sabreauto_defconfig
index 0065a34..386cc54 100644
--- a/configs/mx6sabreauto_defconfig
+++ b/configs/mx6sabreauto_defconfig
@@ -104,3 +104,5 @@
 # CONFIG_VIDEO_BPP32 is not set
 CONFIG_SYS_WHITE_ON_BLACK=y
 CONFIG_VIDEO_IPUV3=y
+CONFIG_SPLASH_SCREEN=y
+CONFIG_SPLASH_SCREEN_ALIGN=y