Add validation column for threat models

[gowthamsk-arm]

Signed-off-by: Gowtham Suresh Kumar gowtham.sureshkumar@arm.com

[gowthamsk-arm]

N/A is for test cases that are out of scope for Parsec testing. We have tickets created for tests with -. These will be added in future and updated in the book.

[ionut-arm]

We have tickets created for tests with -

Could you use a link to those tickets instead of -?

[gowthamsk-arm]

Not required.