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/pinctrl/starfive/Makefile b/drivers/pinctrl/starfive/Makefile
index a4a1206..1503153 100644
--- a/drivers/pinctrl/starfive/Makefile
+++ b/drivers/pinctrl/starfive/Makefile
@@ -1,6 +1,6 @@
 
 # SPDX-License-Identifier: GPL-2.0
 # Core
-obj-$(CONFIG_$(SPL_TPL_)PINCTRL_STARFIVE) += pinctrl-starfive.o
+obj-$(CONFIG_$(PHASE_)PINCTRL_STARFIVE) += pinctrl-starfive.o
 # SoC Drivers
-obj-$(CONFIG_$(SPL_TPL_)PINCTRL_STARFIVE_JH7110)	+= pinctrl-jh7110-sys.o pinctrl-jh7110-aon.o
+obj-$(CONFIG_$(PHASE_)PINCTRL_STARFIVE_JH7110)	+= pinctrl-jh7110-sys.o pinctrl-jh7110-aon.o