board: Use CONFIG_XPL_BUILD instead of CONFIG_SPL_BUILD

Use the new symbol to refer to any 'SPL' build, including TPL and VPL

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/board/lg/x3-t30/Makefile b/board/lg/x3-t30/Makefile
index 3eeb132..fb2527f 100644
--- a/board/lg/x3-t30/Makefile
+++ b/board/lg/x3-t30/Makefile
@@ -6,6 +6,6 @@
 #  (C) Copyright 2021
 #  Svyatoslav Ryhel <clamor95@gmail.com>
 
-obj-$(CONFIG_SPL_BUILD) += x3-t30-spl.o
+obj-$(CONFIG_XPL_BUILD) += x3-t30-spl.o
 
 obj-y += x3-t30.o