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/drivers/core/Makefile b/drivers/core/Makefile
index 20dbff6..9ea5791 100644
--- a/drivers/core/Makefile
+++ b/drivers/core/Makefile
@@ -3,14 +3,14 @@
 # Copyright (c) 2013 Google, Inc
 
 obj-y	+= device.o fdtaddr.o lists.o root.o uclass.o util.o tag.o
-obj-$(CONFIG_$(SPL_TPL_)ACPIGEN) += acpi.o
-obj-$(CONFIG_$(SPL_TPL_)DEVRES) += devres.o
-obj-$(CONFIG_$(SPL_TPL_)DM_DEVICE_REMOVE)	+= device-remove.o
+obj-$(CONFIG_$(PHASE_)ACPIGEN) += acpi.o
+obj-$(CONFIG_$(PHASE_)DEVRES) += devres.o
+obj-$(CONFIG_$(PHASE_)DM_DEVICE_REMOVE)	+= device-remove.o
 obj-$(CONFIG_$(XPL_)SIMPLE_BUS)	+= simple-bus.o
 obj-$(CONFIG_SIMPLE_PM_BUS)	+= simple-pm-bus.o
 obj-$(CONFIG_DM)	+= dump.o
-obj-$(CONFIG_$(SPL_TPL_)REGMAP)	+= regmap.o
-obj-$(CONFIG_$(SPL_TPL_)SYSCON)	+= syscon-uclass.o
+obj-$(CONFIG_$(PHASE_)REGMAP)	+= regmap.o
+obj-$(CONFIG_$(PHASE_)SYSCON)	+= syscon-uclass.o
 obj-$(CONFIG_$(XPL_)OF_LIVE) += of_access.o of_addr.o
 ifndef CONFIG_DM_DEV_READ_INLINE
 obj-$(CONFIG_OF_CONTROL) += read.o