This is a first version of the AHCI driver. It supports SATA HDDs
with UDMA-133 only, up to 6 Gbps and native command queueing.
The more blocks one transfers with one command, the higher is the
chance that the driver produces a fatal handshake error. Nevertheless
the driver is stable with one block per ATA command. Although NCQ is
used the driver doesn't queue multiple commands simultanously.
The driver was tested with a western digital HDD "WDC WD2500BEVS-08VAT1
13.01A13" (250 GB) with hw_arndale (run/ahci) and foc_arndale
(run/ahci, run/l4linux: dd). SSDs were not tested.
Fix#706
