In the last Tech-Forum, Lauren Wehrmeister and I presented our work on adding Arm v8-R64 support to the TF-A codebase.  Our presentation will be added to the Tech-Forum page (TF-A open Tech Forum regular call - Trusted Firmware) shortly.  In the meantime, however, there are more details about the patches here:

https://developer.trustedfirmware.org/w/tf_a/rclasssupportdocs/