Update license headers

Update all license headers to the correct years.

Change-Id: I18881cbceabe26066d69d8535bb3cb969cbaeba1
diff --git a/cmake/helpers.cmake b/cmake/helpers.cmake
index 686488b..389deb9 100644
--- a/cmake/helpers.cmake
+++ b/cmake/helpers.cmake
@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2020 Arm Limited. All rights reserved.
+# Copyright (c) 2020-2021 Arm Limited. All rights reserved.
 #
 # SPDX-License-Identifier: Apache-2.0
 #