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/powerpc/lib/Makefile b/arch/powerpc/lib/Makefile
index ecc2aba..f797f8c 100644
--- a/arch/powerpc/lib/Makefile
+++ b/arch/powerpc/lib/Makefile
@@ -9,7 +9,7 @@
 
 MINIMAL=
 
-ifdef CONFIG_SPL_BUILD
+ifdef CONFIG_XPL_BUILD
 ifndef CONFIG_TPL_BUILD
 ifdef CONFIG_SPL_INIT_MINIMAL
 MINIMAL=y
@@ -45,6 +45,6 @@
 obj-y	+= traps.o
 endif # not minimal
 
-ifdef CONFIG_SPL_BUILD
+ifdef CONFIG_XPL_BUILD
 obj-$(CONFIG_$(SPL_TPL)_FRAMEWORK) += spl.o
 endif