[coreboot] v3 __func0 cleanup

[Myles Watson]

This patch documents the unreadable function in northbridge/amd/k8/pci.c and
cleans up the NULL pointer protection.

Signed-off-by: Myles Watson

It also begs the question why cpu_bus_scan and cpu_bus_init aren't needed in
v3.  They aren't called.  Is that an oversight, or should they be removed.

Thanks,
Myles