Name: Family 17h (Models 00h-0fh) PCIe GPP Bridge
This is a port on one of the 16-lane PCIe GPP controllers.
On the Ryzen 7 1700 with 2 GPUs and a M.2 NVMe drive attached, there are 2 x 8-lane bridges (00:03.1 -> first GPU and 00:03.2 -> second GPU) and 2 x 4-lane bridges (00:01.1 -> NVMe and 00:01.3 -> FCH).
Note that it would appear that all ports on a controller operate at the speed of the slowest port - i.e. using a 2.5GT/s GPU on one of the x8 ports will slow the other port to 2.5GT/s, even if an 8GT/s GPU is on that port.