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/riscv/lib/Makefile b/arch/riscv/lib/Makefile
index 34b69c1..6081181 100644
--- a/arch/riscv/lib/Makefile
+++ b/arch/riscv/lib/Makefile
@@ -40,11 +40,11 @@
 extra-$(CONFIG_CMD_BOOTEFI_SELFTEST) += $(EFI_CRT0) $(EFI_RELOC)
 extra-$(CONFIG_EFI) += $(EFI_CRT0) $(EFI_RELOC)
 
-obj-$(CONFIG_$(SPL_TPL_)USE_ARCH_MEMSET) += memset.o
-obj-$(CONFIG_$(SPL_TPL_)USE_ARCH_MEMMOVE) += memmove.o
-obj-$(CONFIG_$(SPL_TPL_)USE_ARCH_MEMCPY) += memcpy.o
-obj-$(CONFIG_$(SPL_TPL_)USE_ARCH_STRLEN) += strlen_zbb.o
-obj-$(CONFIG_$(SPL_TPL_)USE_ARCH_STRCMP) += strcmp_zbb.o
-obj-$(CONFIG_$(SPL_TPL_)USE_ARCH_STRNCMP) += strncmp_zbb.o
+obj-$(CONFIG_$(PHASE_)USE_ARCH_MEMSET) += memset.o
+obj-$(CONFIG_$(PHASE_)USE_ARCH_MEMMOVE) += memmove.o
+obj-$(CONFIG_$(PHASE_)USE_ARCH_MEMCPY) += memcpy.o
+obj-$(CONFIG_$(PHASE_)USE_ARCH_STRLEN) += strlen_zbb.o
+obj-$(CONFIG_$(PHASE_)USE_ARCH_STRCMP) += strcmp_zbb.o
+obj-$(CONFIG_$(PHASE_)USE_ARCH_STRNCMP) += strncmp_zbb.o
 
-obj-$(CONFIG_$(SPL_TPL_)SEMIHOSTING) += semihosting.o
+obj-$(CONFIG_$(PHASE_)SEMIHOSTING) += semihosting.o