doc: documenting the boot protocol

[dpsmith]

This is an attempt to formalize the boot protocol while also proposing a new name for this implementation of the Secure Loader for SKINIT.

Signed-off-by: Daniel P. Smith [email protected]

[dpsmith]

I have trimmed out the implementation details, addressed the comments, and made a few small expansions. I have pushed the changes to the boot protocol doc and have the implementation details in an in progress document. Even if everyone agrees with this revision, I would like to hold this PR until I can get the implementation document done so that we can ensure they are aligned with each other before merging.