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/ivybridge/Makefile b/arch/x86/cpu/ivybridge/Makefile
index 1f3b0c0..471ad8d 100644
--- a/arch/x86/cpu/ivybridge/Makefile
+++ b/arch/x86/cpu/ivybridge/Makefile
@@ -5,15 +5,15 @@
 ifdef CONFIG_HAVE_FSP
 obj-y += fsp_configs.o ivybridge.o
 else
-obj-$(CONFIG_$(SPL_)X86_32BIT_INIT) += cpu.o
+obj-$(CONFIG_$(XPL_)X86_32BIT_INIT) += cpu.o
 obj-y += early_me.o
 obj-y += lpc.o
 obj-y += northbridge.o
 ifndef CONFIG_XPL_BUILD
 obj-y += sata.o
 endif
-obj-$(CONFIG_$(SPL_)X86_32BIT_INIT) += sdram.o
-ifndef CONFIG_$(SPL_)X86_32BIT_INIT
+obj-$(CONFIG_$(XPL_)X86_32BIT_INIT) += sdram.o
+ifndef CONFIG_$(XPL_)X86_32BIT_INIT
 obj-y += sdram_nop.o
 endif
 endif