global: Rename SPL_ to XPL_

Use XPL_ as the symbol to indicate an SPL build. This means that SPL_ is
no-longer set.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/x86/cpu/intel_common/Makefile b/arch/x86/cpu/intel_common/Makefile
index 2e312a3..d2db589 100644
--- a/arch/x86/cpu/intel_common/Makefile
+++ b/arch/x86/cpu/intel_common/Makefile
@@ -26,10 +26,10 @@
 obj-y += fast_spi.o
 obj-y += lpc.o
 obj-y += lpss.o
-obj-$(CONFIG_$(SPL_)INTEL_GENERIC_WIFI) += generic_wifi.o
+obj-$(CONFIG_$(XPL_)INTEL_GENERIC_WIFI) += generic_wifi.o
 ifndef CONFIG_EFI_APP
 obj-$(CONFIG_$(SPL_TPL_)X86_32BIT_INIT) += microcode.o
-ifndef CONFIG_$(SPL_)X86_64
+ifndef CONFIG_$(XPL_)X86_64
 obj-y += microcode.o
 endif
 endif