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/CZ.NIC/turris_omnia/Makefile b/board/CZ.NIC/turris_omnia/Makefile
index d1ef5cb..acaa3b8 100644
--- a/board/CZ.NIC/turris_omnia/Makefile
+++ b/board/CZ.NIC/turris_omnia/Makefile
@@ -4,4 +4,4 @@
 
 obj-y	:= turris_omnia.o ../turris_atsha_otp.o ../turris_common.o
 obj-$(CONFIG_CMD_EEPROM_LAYOUT)	+= eeprom.o
-obj-$(CONFIG_SPL_BUILD)		+= old_ddr3_training.o
+obj-$(CONFIG_XPL_BUILD)		+= old_ddr3_training.o