feat(cert_create): define the cca chain of trust

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

> make COT=cca

Signed-off-by: Lauren Wehrmeister <lauren.wehrmeister@arm.com>
Change-Id: I123c0a841f67434633a3123cc1fa3e2318585482
diff --git a/tools/cert_create/Makefile b/tools/cert_create/Makefile
index ca548b8..d951286 100644
--- a/tools/cert_create/Makefile
+++ b/tools/cert_create/Makefile
@@ -35,6 +35,8 @@
   include src/tbbr/tbbr.mk
 else ifeq (${COT},dualroot)
   include src/dualroot/cot.mk
+else ifeq (${COT},cca)
+  include src/cca/cot.mk
 else
   $(error Unknown chain of trust ${COT})
 endif