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/common/spl/Makefile b/common/spl/Makefile
index 10528b3..75123eb 100644
--- a/common/spl/Makefile
+++ b/common/spl/Makefile
@@ -7,35 +7,35 @@
 #
 
 ifdef CONFIG_XPL_BUILD
-obj-$(CONFIG_$(SPL_TPL_)FRAMEWORK) += spl.o
-obj-$(CONFIG_$(SPL_TPL_)BOOTROM_SUPPORT) += spl_bootrom.o
-obj-$(CONFIG_$(SPL_TPL_)LOAD_FIT) += spl_fit.o
-obj-$(CONFIG_$(SPL_TPL_)BLK_FS) += spl_blk_fs.o
-obj-$(CONFIG_$(SPL_TPL_)LEGACY_IMAGE_FORMAT) += spl_legacy.o
-obj-$(CONFIG_$(SPL_TPL_)NOR_SUPPORT) += spl_nor.o
-obj-$(CONFIG_$(SPL_TPL_)XIP_SUPPORT) += spl_xip.o
-obj-$(CONFIG_$(SPL_TPL_)YMODEM_SUPPORT) += spl_ymodem.o
+obj-$(CONFIG_$(PHASE_)FRAMEWORK) += spl.o
+obj-$(CONFIG_$(PHASE_)BOOTROM_SUPPORT) += spl_bootrom.o
+obj-$(CONFIG_$(PHASE_)LOAD_FIT) += spl_fit.o
+obj-$(CONFIG_$(PHASE_)BLK_FS) += spl_blk_fs.o
+obj-$(CONFIG_$(PHASE_)LEGACY_IMAGE_FORMAT) += spl_legacy.o
+obj-$(CONFIG_$(PHASE_)NOR_SUPPORT) += spl_nor.o
+obj-$(CONFIG_$(PHASE_)XIP_SUPPORT) += spl_xip.o
+obj-$(CONFIG_$(PHASE_)YMODEM_SUPPORT) += spl_ymodem.o
 ifndef CONFIG_SPL_UBI
-obj-$(CONFIG_$(SPL_TPL_)NAND_SUPPORT) += spl_nand.o
-obj-$(CONFIG_$(SPL_TPL_)ONENAND_SUPPORT) += spl_onenand.o
+obj-$(CONFIG_$(PHASE_)NAND_SUPPORT) += spl_nand.o
+obj-$(CONFIG_$(PHASE_)ONENAND_SUPPORT) += spl_onenand.o
 endif
-obj-$(CONFIG_$(SPL_TPL_)UBI) += spl_ubi.o
-obj-$(CONFIG_$(SPL_TPL_)NET) += spl_net.o
-obj-$(CONFIG_$(SPL_TPL_)MMC) += spl_mmc.o
-obj-$(CONFIG_$(SPL_TPL_)ATF) += spl_atf.o
-obj-$(CONFIG_$(SPL_TPL_)OPTEE_IMAGE) += spl_optee.o
-obj-$(CONFIG_$(SPL_TPL_)OPENSBI) += spl_opensbi.o
-obj-$(CONFIG_$(SPL_TPL_)USB_STORAGE) += spl_usb.o
-obj-$(CONFIG_$(SPL_TPL_)FS_FAT) += spl_fat.o
-obj-$(CONFIG_$(SPL_TPL_)FS_EXT4) += spl_ext.o
-obj-$(CONFIG_$(SPL_TPL_)LOAD_IMX_CONTAINER) += spl_imx_container.o
-obj-$(CONFIG_$(SPL_TPL_)SATA) += spl_sata.o
-obj-$(CONFIG_$(SPL_TPL_)NVME) += spl_nvme.o
-obj-$(CONFIG_$(SPL_TPL_)SEMIHOSTING) += spl_semihosting.o
-obj-$(CONFIG_$(SPL_TPL_)DFU) += spl_dfu.o
-obj-$(CONFIG_$(SPL_TPL_)SPI_LOAD) += spl_spi.o
-obj-$(CONFIG_$(SPL_TPL_)RAM_SUPPORT) += spl_ram.o
-obj-$(CONFIG_$(SPL_TPL_)USB_SDP_SUPPORT) += spl_sdp.o
+obj-$(CONFIG_$(PHASE_)UBI) += spl_ubi.o
+obj-$(CONFIG_$(PHASE_)NET) += spl_net.o
+obj-$(CONFIG_$(PHASE_)MMC) += spl_mmc.o
+obj-$(CONFIG_$(PHASE_)ATF) += spl_atf.o
+obj-$(CONFIG_$(PHASE_)OPTEE_IMAGE) += spl_optee.o
+obj-$(CONFIG_$(PHASE_)OPENSBI) += spl_opensbi.o
+obj-$(CONFIG_$(PHASE_)USB_STORAGE) += spl_usb.o
+obj-$(CONFIG_$(PHASE_)FS_FAT) += spl_fat.o
+obj-$(CONFIG_$(PHASE_)FS_EXT4) += spl_ext.o
+obj-$(CONFIG_$(PHASE_)LOAD_IMX_CONTAINER) += spl_imx_container.o
+obj-$(CONFIG_$(PHASE_)SATA) += spl_sata.o
+obj-$(CONFIG_$(PHASE_)NVME) += spl_nvme.o
+obj-$(CONFIG_$(PHASE_)SEMIHOSTING) += spl_semihosting.o
+obj-$(CONFIG_$(PHASE_)DFU) += spl_dfu.o
+obj-$(CONFIG_$(PHASE_)SPI_LOAD) += spl_spi.o
+obj-$(CONFIG_$(PHASE_)RAM_SUPPORT) += spl_ram.o
+obj-$(CONFIG_$(PHASE_)USB_SDP_SUPPORT) += spl_sdp.o
 endif
 
-obj-$(CONFIG_$(SPL_TPL_)UPL) += spl_upl.o
+obj-$(CONFIG_$(PHASE_)UPL) += spl_upl.o