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/freescale/imx93_evk/Makefile b/board/freescale/imx93_evk/Makefile
index ede8d20..b077acc 100644
--- a/board/freescale/imx93_evk/Makefile
+++ b/board/freescale/imx93_evk/Makefile
@@ -6,7 +6,7 @@
 
 obj-y += imx93_evk.o
 
-ifdef CONFIG_SPL_BUILD
+ifdef CONFIG_XPL_BUILD
 obj-y += spl.o
 obj-$(CONFIG_IMX93_EVK_LPDDR4X) += lpddr4x_timing.o lpddr4x_timing_1866mts.o
 endif