feat(tpm): add tpm drivers and framework

Add tpm2 drivers to tf-a with adequate framework
-implement a fifo spi interface that works
 with discrete tpm chip.
-implement tpm command layer interfaces that are used
 to initialize, start and make measurements and
 close the interface.
-tpm drivers are built using their own make file
 to allow for ease in porting across platforms,
 and across different interfaces.

Signed-off-by: Tushar Khandelwal <tushar.khandelwal@arm.com>
Signed-off-by: Abhi Singh <abhi.singh@arm.com>
Change-Id: Ie1a189f45c80f26f4dea16c3bd71b1503709e0ea
diff --git a/make_helpers/defaults.mk b/make_helpers/defaults.mk
index ec2aa1b..906e5d7 100644
--- a/make_helpers/defaults.mk
+++ b/make_helpers/defaults.mk
@@ -192,6 +192,9 @@
 # Option to build TF with Measured Boot support
 MEASURED_BOOT			:= 0
 
+# Option to build TF with Discrete TPM support
+DISCRETE_TPM			:= 0
+
 # Option to enable the DICE Protection Environmnet as a Measured Boot backend
 DICE_PROTECTION_ENVIRONMENT	:=0