[crypto] adding ARM PSA (Platform Security Architecture) support (#6862)

- New format for MAC keys, as a union between literal key and keyrefs.
- Modified key_manager to handle both literal keys or keyrefs.
- Modified MAC and sub_mac modules to handle both Literal Keys or keyrefs.
- Updated Crypto Modules to use abstracted APIs.
- New CLIs to handle networkkey and pskc references.

src/cli/cli_dataset.cpp

@@ -692,6 +692,8 @@ otError Dataset::ProcessPskc(Arg aArgs[])
 
     if (aArgs[0].IsEmpty())
     {
+        // sDataset holds the key as a literal string, we don't
+        // need to export it from PSA ITS.
         if (sDataset.mComponents.mIsPskcPresent)
         {
             mInterpreter.OutputBytes(sDataset.mPskc.m8);