ITS: Add support for encrypted ITS

-Adds encryption and authentication support for ITS files
-Encryption is optional and is enabled using a CMake variable
-The encryption implementation is platform dependent,
 the signatures of the APIs are provided in this change

Change-Id: Ifd3a67ac2274fa8d7ceec19482f7cec01b2cac54
Signed-off-by: Markus Swarowsky <markus.swarowsky@nordicsemi.no>
17 files changed