Update license headers

Update all license headers to the correct years.

Change-Id: I18881cbceabe26066d69d8535bb3cb969cbaeba1
diff --git a/targets/corstone-300/target.cpp b/targets/corstone-300/target.cpp
index d5c44ea..e5f4680 100644
--- a/targets/corstone-300/target.cpp
+++ b/targets/corstone-300/target.cpp
@@ -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
  *