[coreboot] Test SeaBIOS AHCI support

[Rudolf Marek]

Hi,

I think SATA port 4 and 5 may have some issues on SB700 (not detecting drive in 
linux and seabios)

Dunno why. I did not have time to try AHCI mode yet. But I think we can drop the 
wait for non BSY in coreboot beacuse the payload/linux should do that.

(the sata_drive_detect)

Thanks,
Rudolf