global: Rename SPL_TPL_ to PHASE_

Use PHASE_ as the symbol to select a particular XPL build. This means
that SPL_TPL_ is no-longer set.

Update the comment in bootstage to refer to this symbol, instead of
SPL_

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/x86/cpu/broadwell/Makefile b/arch/x86/cpu/broadwell/Makefile
index 6c6d0ed..dfe013e 100644
--- a/arch/x86/cpu/broadwell/Makefile
+++ b/arch/x86/cpu/broadwell/Makefile
@@ -2,8 +2,8 @@
 #
 # Copyright (c) 2016 Google, Inc
 
-obj-$(CONFIG_$(SPL_TPL_)X86_16BIT_INIT) += cpu.o
-obj-$(CONFIG_$(SPL_TPL_)X86_32BIT_INIT) += cpu_full.o
+obj-$(CONFIG_$(PHASE_)X86_16BIT_INIT) += cpu.o
+obj-$(CONFIG_$(PHASE_)X86_32BIT_INIT) += cpu_full.o
 
 ifdef CONFIG_SPL
 ifndef CONFIG_XPL_BUILD
@@ -18,7 +18,7 @@
 endif
 endif
 
-ifeq ($(CONFIG_$(SPL_TPL_)X86_32BIT_INIT),)
+ifeq ($(CONFIG_$(PHASE_)X86_32BIT_INIT),)
 #obj-y += cpu_from_spl.o
 endif
 
@@ -29,5 +29,5 @@
 obj-y += pch.o
 obj-y += pinctrl_broadwell.o
 obj-y += power_state.o
-obj-$(CONFIG_$(SPL_TPL_)X86_32BIT_INIT) += refcode.o
-obj-$(CONFIG_$(SPL_TPL_)X86_32BIT_INIT) += sdram.o
+obj-$(CONFIG_$(PHASE_)X86_32BIT_INIT) += refcode.o
+obj-$(CONFIG_$(PHASE_)X86_32BIT_INIT) += sdram.o