We working on a project where we would also like to build TF-A for TX2 to provide a key management service. We do not need a Trusted OS such as Trusty but would simply like to use Trustzone to manage encryption keys. Like user 53216142 we are interested in knowing how the TF-A SW can be integrated to the TX2 boot flow to replace the TOS.img.
We have not open sourced ATF source code yet. But we contribute to ARM ATF source. I will check internally if upstream ATF should boot on TX2 or not. In that case, you can download and build and replace TOS.img with your binary