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

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

Like 9db2f8b4410f66c3d8d3c6a91c200efaf3ac7a39 (ahci: Enable SB600 64bit
DMA on MSI K9A2 Platinum) and c12cac89b25894f673b5fc2e71138926995474d7
(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>