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-uniphier/Makefile b/arch/arm/mach-uniphier/Makefile
index 5172efa..d1ec819 100644
--- a/arch/arm/mach-uniphier/Makefile
+++ b/arch/arm/mach-uniphier/Makefile
@@ -1,6 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0+
 
-ifdef CONFIG_SPL_BUILD
+ifdef CONFIG_XPL_BUILD
 
 obj-y += boards.o
 obj-y += spl_board_init.o