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/Makefile b/arch/arm/mach-at91/Makefile
index cbd0ed6..447cd80 100644
--- a/arch/arm/mach-at91/Makefile
+++ b/arch/arm/mach-at91/Makefile
@@ -1,7 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0+
 
 obj-$(CONFIG_AT91_WANTS_COMMON_PHY) += phy.o
-ifneq ($(CONFIG_SPL_BUILD),)
+ifneq ($(CONFIG_XPL_BUILD),)
 obj-$(CONFIG_AT91SAM9260) += sdram.o spl_at91.o
 obj-$(CONFIG_AT91SAM9G20) += sdram.o spl_at91.o
 obj-$(CONFIG_AT91SAM9M10G45) += mpddrc.o spl_at91.o