Add SPDX license identifiers

Adds one SPDX-License-Identifier line [1] to each source files that
contains license text.

Generated by [2]:
  spdxify.py --add-spdx optee_os/

The scancode tool [3] was used to double check the license matching
code in the Python script. All the licenses detected by scancode are
either detected by spdxify.py, or have no SPDX identifier, or are false
matches.

Link: [1] https://spdx.org/licenses/
Link: [2] https://github.com/jforissier/misc/blob/f7b56c8/spdxify.py
Link: [3] https://github.com/nexB/scancode-toolkit
Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Acked-by: Joakim Bech <joakim.bech@linaro.org>
diff --git a/scripts/symbolize.py b/scripts/symbolize.py
index 77f842f..e26e493 100755
--- a/scripts/symbolize.py
+++ b/scripts/symbolize.py
@@ -1,4 +1,5 @@
 #!/usr/bin/env python
+# SPDX-License-Identifier: BSD-2-Clause
 #
 # Copyright (c) 2017, Linaro Limited
 # All rights reserved.