[TF-M] [RFC] The veneer usage under library model (Ken Liu)

Ken,

This is the answer to "What do you think about this update?"

When external TF-M APIs do not change, there should be no user impact. As the veneer is just an internal implementation of parameter passing, changing the veneer implementation would be just fine.

I made some suggestions here https://lists.trustedfirmware.org/pipermail/tf-m/2020-March/000805.html

I would be happy to review your implementation in case that you have doubts.

Best regards Reinhard