cert_create: Define the dualroot CoT

Selection of the chain of trust is done through the COT build option:

> make COT=dualroot

Change-Id: Id87c7a5116bdd13bdb29645ecf31d111ad094c1e
Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>
diff --git a/tools/cert_create/src/dualroot/cot.mk b/tools/cert_create/src/dualroot/cot.mk
new file mode 100644
index 0000000..a572484
--- /dev/null
+++ b/tools/cert_create/src/dualroot/cot.mk
@@ -0,0 +1,10 @@
+#
+# Copyright (c) 2020, Arm Limited. All rights reserved.
+#
+# SPDX-License-Identifier: BSD-3-Clause
+#
+
+PLAT_MSG		:=	Dual root of trust
+PLAT_INCLUDE		:=	../../include/tools_share
+
+OBJECTS += src/dualroot/cot.o