Linux uses the term AMD64 to describe the 64 bit versions of the OS usually.
Since the Ryzen model is indeed capable of running in AMD64 mode therefor it is supported somewhat.
I suspect in a a year it will be much more well supported. There are new changes in that processor that I don't think have been fully incorporated into 4.11 yet.
Ubuntu offers out of package kernels for testing and general use.
http://kernel.ubuntu.com/~kernel-ppa/mainline/
It's pretty easy to load up a new kernel but if you have a stock 16.04 you may have to fool with it a bit to get the newer kernels on.
