Thanks to AMD Italia, now we know that the AMD PSP vulnerability is - actually - a non existent problem. First of all, in order to take advantage of this exploit, an hacker has to have physical access to the server.
Consequently, he has to update/replace the SPI-Flash manually. SPI-Flash can't be flashed from OS or remotely. In other words, this vulnerability isn't subject to remote code execution.
So, the hype among the forums about a new "Meltdown bug" AMD-Only is 100% wrong. However, AMD and its partners are working on a fix, available during this month, in order to cancel even this remote event.