That earlier article was basically an open-ended story after the oclHashcat project tweeted, "Just found in current AMD drivers (libs are not stripped): "nm /usr/lib/libamdocl64.so | grep -i backdoor" -> ... osTestBackdoorATI."
After we drew attention to that tweet, Graham Sellers at AMD said that it was "a hook used by our automated tests to access memory usage statistics from the driver."
James Prior of AMD's Global Communication has now emailed me this afternoon with AMD's official statement over the "osTestBackdoorATI" reference:
"The symbol found inside libamdocl64.so is a non-functional test point and AMD is confident end user security has not been compromised. This, and other, test points will be removed from public libraries in all future releases."