arch: 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/arch/arm/mach-imx/mx6/opos6ul.c b/arch/arm/mach-imx/mx6/opos6ul.c
index 340e614..6a79dcb 100644
--- a/arch/arm/mach-imx/mx6/opos6ul.c
+++ b/arch/arm/mach-imx/mx6/opos6ul.c
@@ -79,7 +79,7 @@
 	return 0;
 }
 
-#ifdef CONFIG_SPL_BUILD
+#ifdef CONFIG_XPL_BUILD
 #include <asm/arch/mx6-ddr.h>
 #include <linux/libfdt.h>
 #include <spl.h>
@@ -210,4 +210,4 @@
 	/* DDR initialization */
 	spl_dram_init();
 }
-#endif /* CONFIG_SPL_BUILD */
+#endif /* CONFIG_XPL_BUILD */