Se api

Just for preview. Please don't merge it.
So the question is if we would like to make this the programmers responsibility to make sure this doesn't happen or not. I think it's a tiny cost of adding this check and wonder if we really have to set *aid to NULL in the release function?
- If you set it to NULL there and then call aid_create, things will work, which is fine ...
- If you don't set it to NULL in the release function and call aid_create again using same pointer, then TEE_ASSERT will assert and you catch the problem, which also is fine (a fix will be needed from the caller of course).