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/topic/zynq/Makefile b/board/topic/zynq/Makefile
index cc100b0..23a6dd8 100644
--- a/board/topic/zynq/Makefile
+++ b/board/topic/zynq/Makefile
@@ -6,4 +6,4 @@
 # Remove quotes
 hw-platform-y :=$(shell echo $(CONFIG_DEFAULT_DEVICE_TREE))
 
-obj-$(CONFIG_SPL_BUILD) += $(hw-platform-y)/ps7_init_gpl.o
+obj-$(CONFIG_XPL_BUILD) += $(hw-platform-y)/ps7_init_gpl.o