Only touch PCI functions > 0 on multi-function devices; rescan max pci each time.

Only touch PCI functions > 0 on multi-function devices; rescan max pci each time.

Some single-function devices will respond to all sub-functions - and
    this confuses things.  So, when scanning the PCI bus make sure to
    only touch function 0 on single-function devices.
Since the bus scanning code is necessarily complex now, we might as
    well implement max bus detection inline with all pci scans.  So,
    there is no need to scan for the max bus at startup.