[TF-A] Errata framework proposal

Hi all,

As presented on this week's tech forum, I have recently been working on a framework to improve errata implementations, consolidate the disparate requirements around them, and make errata information available at runtime. This is related, but separate to the errata ABI which is being worked on by Sona. Patches are available for review [1] and feedback is welcome.

This email is to host discussion around the proposal, especially things that came up during the tech forum. The team would like to merge this sometime in April, but the sooner it is accepted, the sooner we can start (and complete!) the migration.

[1]: https://review.trustedfirmware.org/q/topic:%22bk%252Ferrata_refactor%22+