The hardware codec support removal is a bone headed decision. The first sale doctrine (among other things) says that if you sell a patented device, you are implicitly selling a transferrable patent license that allows use of that one physical device.
So, there are two possibilities for patent infringement:
1) AMD licensed a patent that allows them to write software that accesses hardware capabilities using software drivers. This is already ludicrous, but the US patent system is in play. Furthermore, the third party patent holder is asserting that AMD's license only applies to Windows drivers.
2) AMD's hardware violates a third party patent.
In both cases, this is AMD's problem, not the Linux distribution's. Also, no one is claiming either of the above things have happened.
(Not a lawyer, but this is basic IP law.)