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/avionic-design/tec-ng/Makefile b/board/avionic-design/tec-ng/Makefile
index d6890e5..ec1710e 100644
--- a/board/avionic-design/tec-ng/Makefile
+++ b/board/avionic-design/tec-ng/Makefile
@@ -3,6 +3,6 @@
 # (C) Copyright 2013
 # Avionic Design GmbH <www.avionic-design.de>
 
-obj-$(CONFIG_SPL_BUILD) += tec-ng-spl.o
+obj-$(CONFIG_XPL_BUILD) += tec-ng-spl.o
 
 obj-y	+= ../common/tamonten-ng.o