ata_piix: port enable for the first SATA controller of ICH8 is 0xf not 0x3

ICH8 and 9 use two SFF controllers to show 6 SATA ports.  The first
controllre hosts the first 4 ports while the second one hosts the last
2.  The PCS register of the first controller encompasses the first
four ports or all six ports depending on configuration while PCS of
the second controller controls the last two ports.  Using 0xf for the
first controller and 0x3 for the second controller always result in
the correct configuration.

Signed-off-by: Tejun Heo <htejun@gmail.com>