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/colibri_imx7_defconfig b/configs/colibri_imx7_defconfig
index ae58505..f33ca11 100644
--- a/configs/colibri_imx7_defconfig
+++ b/configs/colibri_imx7_defconfig
@@ -91,5 +91,7 @@
 CONFIG_USB_GADGET_DOWNLOAD=y
 CONFIG_DM_VIDEO=y
 CONFIG_SYS_WHITE_ON_BLACK=y
+CONFIG_SPLASH_SCREEN=y
+CONFIG_SPLASH_SCREEN_ALIGN=y
 CONFIG_OF_LIBFDT_OVERLAY=y
 CONFIG_FDT_FIXUP_PARTITIONS=y