Vincent Stehlé

Moving to draft after [call of 11 Mar](https://github.com/ARM-software/ebbr/wiki/EBBR-Notes-2024.03.11).

Adapt a bit to stay compatible with [dependable boot](https://gitlab.com/Linaro/trustedsubstrate/mbfw/uploads/3d0d7d11ca9874dc9115616b418aa330/mbfw.pdf): - Require authenticated fmp firmware updates - Explicitly allow non-firmware updates in any format

Thanks @xypron for your review. As discussed during the call of Jul 1, I have removed the change to `.typos.txt` from this pull request. With that, merging as approved.