ahci: Detect Marvell 88SE9172 SATA controller

The Marvell 88SE9172 SATA controller (PCI ID 1b4b 917a) already worked
once it was detected, but was missing an ahci_pci_tbl entry.

Boot tested on a Gigabyte Z68X-UD3H-B3 motherboard.

Signed-off-by: Matt Johnson <johnso87@illinois.edu>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>