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/tpm/Makefile b/drivers/tpm/Makefile
index 9540fd7..76e516d 100644
--- a/drivers/tpm/Makefile
+++ b/drivers/tpm/Makefile
@@ -1,7 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0+
 # Copyright (c) 2011 The Chromium OS Authors. All rights reserved.
 
-obj-$(CONFIG_$(SPL_TPL_)TPM) += tpm-uclass.o
+obj-$(CONFIG_$(PHASE_)TPM) += tpm-uclass.o
 
 obj-$(CONFIG_TPM_ATMEL_TWI) += tpm_atmel_twi.o
 obj-$(CONFIG_TPM_TIS_INFINEON) += tpm_tis_infineon.o
@@ -10,7 +10,7 @@
 obj-$(CONFIG_TPM_ST33ZP24_I2C) += tpm_tis_st33zp24_i2c.o
 obj-$(CONFIG_TPM_ST33ZP24_SPI) += tpm_tis_st33zp24_spi.o
 
-obj-$(CONFIG_$(SPL_TPL_)TPM2_CR50_I2C) += cr50_i2c.o
+obj-$(CONFIG_$(PHASE_)TPM2_CR50_I2C) += cr50_i2c.o
 obj-$(CONFIG_TPM2_TIS_SANDBOX) += tpm2_tis_sandbox.o sandbox_common.o
 obj-$(CONFIG_TPM2_TIS_SPI) += tpm2_tis_core.o tpm2_tis_spi.o
 obj-$(CONFIG_TPM2_TIS_I2C) += tpm2_tis_core.o tpm2_tis_i2c.o