The AMD SB600 southbridge has an PATA IDE interface, but the
    secondary port has no physical connections, so is disabled in
    the PCI header which makes it appear as a legacy port.

    On most systems this causes no trouble, but the Amigaone X1000 has
    an SB600 connected to a PowerPC SoC PCI-e root port, with an
    emulated ISA bus. On this system a kernel panic occurs at boot
    time during device attach for the secondary port.

    Mark the port as 'dummy' to prevent this. As a bonus, disabling
    this will slightly speed up booting on PC systems using an
    SB600 as they will now skip 2 known empty ports.

Signed-off-by: Darren Stevens <Darren@stevens-zone.net>

Signed-off-by: Tejun Heo <tj@kernel.org>