Build: Make t_cose and QCBOR optional

To avoid errors when not building with the initial attestation partition
enabled, as optional targets are only compiled when they are a
dependency of a non-optional target.

Change-Id: If109ec1b2208c7d9138355f9e346ec1b1a3eb13f
Signed-off-by: Raef Coles <raef.coles@arm.com>
diff --git a/lib/ext/t_cose/CMakeLists.txt b/lib/ext/t_cose/CMakeLists.txt
index d06fc76..762ad05 100644
--- a/lib/ext/t_cose/CMakeLists.txt
+++ b/lib/ext/t_cose/CMakeLists.txt
@@ -1,5 +1,5 @@
 #-------------------------------------------------------------------------------
-# Copyright (c) 2020, Arm Limited. All rights reserved.
+# Copyright (c) 2020-2021, Arm Limited. All rights reserved.
 #
 # SPDX-License-Identifier: BSD-3-Clause
 #
@@ -7,7 +7,7 @@
 
 cmake_minimum_required(VERSION 3.15)
 
-add_library(tfm_t_cose STATIC)
+add_library(tfm_t_cose STATIC EXCLUDE_FROM_ALL)
 
 target_sources(tfm_t_cose
     PRIVATE