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/aristainetos2c_defconfig b/configs/aristainetos2c_defconfig
index 6391453..47f5a2c 100644
--- a/configs/aristainetos2c_defconfig
+++ b/configs/aristainetos2c_defconfig
@@ -111,5 +111,7 @@
 CONFIG_SYS_WHITE_ON_BLACK=y
 CONFIG_DISPLAY=y
 CONFIG_VIDEO_IPUV3=y
+CONFIG_SPLASH_SCREEN=y
+CONFIG_SPLASH_SCREEN_ALIGN=y
 CONFIG_IMX_WATCHDOG=y
 # CONFIG_EFI_LOADER is not set