TIP 002: Trussed backend abstraction

[nickray]

WIP

Goal: Enable configurable crypto (+other) backends for Trussed, unlocking e.g. hardware crypto (e.g., secure elements).

Current dispatch is:

Client --RPC(client_id, method, parameters)--> Trussed --hardcoded dispatch--> Fixed software implementation

Desired dispatch:

Client --RPC(client_id, backend_id, method, parameters)--> Trussed --dispatch by backend ID--> implementation

A follow-on TIP is about how to set everything up.