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-aspeed/ast2600/lowlevel_init.S b/arch/arm/mach-aspeed/ast2600/lowlevel_init.S
index 594963d..d1c3106 100644
--- a/arch/arm/mach-aspeed/ast2600/lowlevel_init.S
+++ b/arch/arm/mach-aspeed/ast2600/lowlevel_init.S
@@ -97,7 +97,7 @@
 .globl lowlevel_init
 
 lowlevel_init:
-#if defined(CONFIG_SPL) && !defined(CONFIG_SPL_BUILD)
+#if defined(CONFIG_SPL) && !defined(CONFIG_XPL_BUILD)
 	mov	pc, lr
 #else
 	/* setup ARM arch timer frequency */