[TF-M] TF-M generic threat model

Hi all,

A generic threat model of TF-M has been uploaded to gerrit. It is a key step in TF-M Threat Modeling.

Please help review the threat model document via the link below. https://review.trustedfirmware.org/c/TF-M/trusted-firmware-m/+/7492 Any question or comment is welcome!

Best regards, Hu Ziji