Hi,
Now I'm stuck at one point: I could definitely identify the SuperIO W83627HF and the northbridge AMD K8, but I have trouble with the southbridge. lspci shows a "VIA K8T800Pro" host bridge, but flashrom shows a "VIA VT8237" chipset. So now I'm not sure how my devicetree has to look like. Do I need to support K8T800p (should be similar to the supported K8T890) and/or do I need the already supportet VT8237?
Most likely, you have both. The K8T800 (or similar) is essentially what was left of the north bridge after the DRAM controller was moved into the CPU. So, it connects the processor's HyperTransport to the AGP slot and to the V-Link to the VT8237 (or similar) south bridge, which in turn connects to all the rest of it (PCI, LPC, SMBus, ...)
The datasheets for both (as bad as they are) should make the general architecture pretty clear.
Florian