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/mtd/spi/Makefile b/drivers/mtd/spi/Makefile
index 2a287a6..44e67cd 100644
--- a/drivers/mtd/spi/Makefile
+++ b/drivers/mtd/spi/Makefile
@@ -3,12 +3,12 @@
 # (C) Copyright 2006
 # Wolfgang Denk, DENX Software Engineering, wd@denx.de.
 
-obj-$(CONFIG_$(SPL_TPL_)DM_SPI_FLASH) += sf-uclass.o
+obj-$(CONFIG_$(PHASE_)DM_SPI_FLASH) += sf-uclass.o
 spi-nor-y := sf_probe.o spi-nor-ids.o
 
 ifdef CONFIG_XPL_BUILD
 obj-$(CONFIG_SPL_SPI_BOOT)	+= fsl_espi_spl.o
-ifeq ($(CONFIG_$(SPL_TPL_)SPI_FLASH_TINY),y)
+ifeq ($(CONFIG_$(PHASE_)SPI_FLASH_TINY),y)
 spi-nor-y += spi-nor-tiny.o
 else
 spi-nor-y += spi-nor-core.o
@@ -19,6 +19,6 @@
 
 obj-$(CONFIG_SPI_FLASH) += spi-nor.o
 obj-$(CONFIG_SPI_FLASH_DATAFLASH) += sf_dataflash.o
-obj-$(CONFIG_$(SPL_TPL_)SPI_FLASH_MTD) += sf_mtd.o
+obj-$(CONFIG_$(PHASE_)SPI_FLASH_MTD) += sf_mtd.o
 obj-$(CONFIG_SPI_FLASH_SANDBOX) += sandbox.o
-obj-$(CONFIG_$(SPL_TPL_)BOOTDEV_SPI_FLASH) += sf_bootdev.o
+obj-$(CONFIG_$(PHASE_)BOOTDEV_SPI_FLASH) += sf_bootdev.o