docs(threat model): add TF-A threat model

This is the first release of the public Trusted
Firmware A class threat model. This release
provides the baseline for future updates to be
applied as required by developments to the
TF-A code base.

Signed-off-by: Zelalem Aweke <zelalem.aweke@arm.com>
Change-Id: I3c9aadc46196837679f0b1377bec9ed4fc42ff11
6 files changed