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-mediatek/mt7629/lowlevel_init.S b/arch/arm/mach-mediatek/mt7629/lowlevel_init.S
index 0a0672c..9f19003 100644
--- a/arch/arm/mach-mediatek/mt7629/lowlevel_init.S
+++ b/arch/arm/mach-mediatek/mt7629/lowlevel_init.S
@@ -16,7 +16,7 @@
 
 ENTRY(lowlevel_init)
 
-#ifndef CONFIG_SPL_BUILD
+#ifndef CONFIG_XPL_BUILD
 	/* Return to U-Boot via saved link register */
 	mov	pc, lr
 #else