Build system: Changes to drive cert_create for dualroot CoT

The build system needs to drive the cert_create tool in a slightly
different manner when using the dualroot chain of trust.

 - It needs to pass it the platform root of trust key file.

 - It must not try to generate the Non-Trusted Firmware Key Certificate,
   which is not part of the dualroot CoT.

Change-Id: Ibcc821c5735765523730f861ae8230208f41302b
Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>

make_helpers/tbbr/tbbr_tools.mk

 #
-# Copyright (c) 2015-2019, ARM Limited and Contributors. All rights reserved.
+# Copyright (c) 2015-2020, ARM Limited and Contributors. All rights reserved.
 #
 # SPDX-License-Identifier: BSD-3-Clause
 #
@@ -23,6 +23,7 @@
 #   KEY_ALG
 #   KEY_SIZE
 #   ROT_KEY
+#   PROT_KEY
 #   TRUSTED_WORLD_KEY
 #   NON_TRUSTED_WORLD_KEY
 #   SCP_BL2_KEY
@@ -57,6 +58,7 @@ $(if ${KEY_SIZE},$(eval $(call CERT_ADD_CMD_OPT,${KEY_SIZE},--key-size)))
 $(if ${HASH_ALG},$(eval $(call CERT_ADD_CMD_OPT,${HASH_ALG},--hash-alg)))
 $(if ${ROT_KEY},$(eval $(call CERT_ADD_CMD_OPT,${ROT_KEY},--rot-key)))
 $(if ${ROT_KEY},$(eval $(call CERT_ADD_CMD_OPT,${ROT_KEY},--rot-key,FWU_)))
+$(if ${PROT_KEY},$(eval $(call CERT_ADD_CMD_OPT,${PROT_KEY},--prot-key)))
 $(if ${TRUSTED_WORLD_KEY},$(eval $(call CERT_ADD_CMD_OPT,${TRUSTED_WORLD_KEY},--trusted-world-key)))
 $(if ${NON_TRUSTED_WORLD_KEY},$(eval $(call CERT_ADD_CMD_OPT,${NON_TRUSTED_WORLD_KEY},--non-trusted-world-key)))
 
@@ -93,5 +95,7 @@ endif
 ifneq (${BL33},)
     $(if ${BL33_KEY},$(eval $(call CERT_ADD_CMD_OPT,${BL33_KEY},--nt-fw-key)))
     $(eval $(call TOOL_ADD_PAYLOAD,${BUILD_PLAT}/nt_fw_content.crt,--nt-fw-cert))
+ifneq (${COT},dualroot)
     $(eval $(call TOOL_ADD_PAYLOAD,${BUILD_PLAT}/nt_fw_key.crt,--nt-fw-key-cert))
 endif
+endif