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/crypto/fsl/Makefile b/drivers/crypto/fsl/Makefile
index 4fbce51..965c493 100644
--- a/drivers/crypto/fsl/Makefile
+++ b/drivers/crypto/fsl/Makefile
@@ -6,6 +6,6 @@
 obj-$(CONFIG_FSL_CAAM) += jr.o fsl_hash.o jobdesc.o error.o
 obj-$(CONFIG_CMD_BLOB)$(CONFIG_IMX_CAAM_DEK_ENCAP) += fsl_blob.o
 obj-$(CONFIG_RSA_FREESCALE_EXP) += fsl_rsa.o
-obj-$(CONFIG_$(SPL_TPL_)FSL_CAAM_RNG) += rng.o
+obj-$(CONFIG_$(PHASE_)FSL_CAAM_RNG) += rng.o
 obj-$(CONFIG_FSL_DCP_RNG) += dcp_rng.o
 obj-$(CONFIG_FSL_MFGPROT) += fsl_mfgprot.o