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/Makefile b/arch/x86/cpu/Makefile
index 8899830..39c8b08 100644
--- a/arch/x86/cpu/Makefile
+++ b/arch/x86/cpu/Makefile
@@ -9,7 +9,7 @@
 ifeq ($(CONFIG_$(XPL_)X86_64),y)
 extra-y	= start64.o
 else
-ifeq ($(CONFIG_$(SPL_TPL_)X86_16BIT_INIT),y)
+ifeq ($(CONFIG_$(PHASE_)X86_16BIT_INIT),y)
 extra-y	= start.o
 else
 ifndef CONFIG_SPL
@@ -24,7 +24,7 @@
 endif
 endif
 
-extra-$(CONFIG_$(SPL_TPL_)X86_16BIT_INIT) += resetvec.o start16.o
+extra-$(CONFIG_$(PHASE_)X86_16BIT_INIT) += resetvec.o start16.o
 
 obj-y	+= cpu.o
 ifndef CONFIG_TPL_BUILD
@@ -54,10 +54,10 @@
 obj-$(CONFIG_INTEL_QUEENSBAY) += queensbay/
 obj-$(CONFIG_INTEL_TANGIER) += tangier/
 obj-$(CONFIG_APIC) += lapic.o ioapic.o
-obj-$(CONFIG_$(SPL_TPL_)ACPI_GPE) += acpi_gpe.o
+obj-$(CONFIG_$(PHASE_)ACPI_GPE) += acpi_gpe.o
 obj-$(CONFIG_QFW) += qfw_cpu.o
 ifndef CONFIG_SYS_COREBOOT
-obj-$(CONFIG_$(SPL_TPL_)X86_32BIT_INIT) += irq.o
+obj-$(CONFIG_$(PHASE_)X86_32BIT_INIT) += irq.o
 endif
 ifndef CONFIG_$(XPL_)X86_64
 obj-$(CONFIG_$(XPL_)SMP) += mp_init.o