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-at91/config.mk b/arch/arm/mach-at91/config.mk
index 5426394..a31612b 100644
--- a/arch/arm/mach-at91/config.mk
+++ b/arch/arm/mach-at91/config.mk
@@ -3,7 +3,7 @@
 endif
 
 ifeq ($(CONFIG_CPU_V7A),y)
-ifndef CONFIG_SPL_BUILD
+ifndef CONFIG_XPL_BUILD
 INPUTS-y	+= u-boot.img
 endif
 endif