ata_piix: only enable the first port on apple macbook pro

ICH8M on apple macbook pro occasionally locks up completely during PCS
initialization if ports other than the first one are enabled.  Add a
separate controller ID and only enable the first port.

tj: commit description added and patch updated to fit with the
    previous controller ID update.

Signed-off-by: Thomas Rohwer <tr@tng.de>
Signed-off-by: Tejun Heo <htejun@gmail.com>