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/compulab/cm_fx6/Makefile b/board/compulab/cm_fx6/Makefile
index e648db2..e9f86cb 100644
--- a/board/compulab/cm_fx6/Makefile
+++ b/board/compulab/cm_fx6/Makefile
@@ -3,7 +3,7 @@
 # (C) Copyright 2014 CompuLab, Ltd. <www.compulab.co.il>
 #
 # Authors: Nikita Kiryanov <nikita@compulab.co.il>
-ifdef CONFIG_SPL_BUILD
+ifdef CONFIG_XPL_BUILD
 obj-y = common.o spl.o
 else
 obj-y = common.o cm_fx6.o