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/x86/cpu/apollolake/Makefile b/arch/x86/cpu/apollolake/Makefile
index 2ddf4af..f481f40 100644
--- a/arch/x86/cpu/apollolake/Makefile
+++ b/arch/x86/cpu/apollolake/Makefile
@@ -2,20 +2,20 @@
 #
 # Copyright 2019 Google LLC
 
-obj-$(CONFIG_SPL_BUILD) += cpu_spl.o
-obj-$(CONFIG_SPL_BUILD) += spl.o
-obj-$(CONFIG_SPL_BUILD) += systemagent.o
+obj-$(CONFIG_XPL_BUILD) += cpu_spl.o
+obj-$(CONFIG_XPL_BUILD) += spl.o
+obj-$(CONFIG_XPL_BUILD) += systemagent.o
 obj-y += cpu_common.o
 
 ifndef CONFIG_TPL_BUILD
 obj-y += cpu.o
 obj-y += punit.o
 obj-y += fsp_bindings.o
-ifdef CONFIG_SPL_BUILD
+ifdef CONFIG_XPL_BUILD
 obj-y += fsp_m.o
 endif
 endif
-ifndef CONFIG_SPL_BUILD
+ifndef CONFIG_XPL_BUILD
 obj-y += acpi.o
 obj-y += fsp_s.o
 endif