Implement public key extraction in TZ backend

Implement public key extraction in TZ backend

Public keys are not secrets and there are scenarios like ECDH when they
have to be extracted in raw form. Exportability logic still applies.

* Separate the object id and the raw data in TZ backend objects.
* Rename function arguments to make their meaning more adequate.
* Use object id when making operations using given key or binary data.
* Return raw data only to CKMLogic via getBinary() method.
* Make getBinary() return an empty buffer for private and symmetric keys.
* Move m_type to AKey where it's used.

Change-Id: Idf6db51387d98f6560f0da18e2fc1d9bbc3abc4f