ahci: Enable SB600 64bit DMA on MSI K9AGM2 (MS-7327) v2

Like e65cc194 (ahci: Enable SB600 64bit
DMA on MSI K9A2 Platinum) and 3c4aa91f
(ahci: Enable SB600 64bit DMA on Asus M3A), this patch enables 64bit DMA
for the AHCI SATA controller of another board that has the SB600
southbridge.

In this case though we're enabling 64bit DMA for another MSI motherboard,
the K9AGM2 or MS-7327. It is new enough that all of the BIOS releases
since the initial release (1.0 from 2007-02-09) work correctly with 64bit
DMA enabled.

Signed-off-by: Mark Nelson <mdnelson8@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>