Review of External Debug Security Spec

[bcstrongx]

This is probably not the best way to advertise this, but I didn't have a better idea.

There is a TG developing a RISC-V extension that would introduce the concept of Debug Mode with only supervisor-level privilege. There was some discussion of the impact to ROM-based implementations (like this one), and what ISA accommodations may be needed. It would be good to have someone who has actually worked on such implementations weigh in. The spec repo is here, while the topic of ROM-based implementations is discussed here.