[libata] AHCI: Add support for Marvell AHCI-like chips (initially 6145)

Add support for the SATA portion of Marvell's AHCI-compatible chips.
The PATA port capability, also available via AHCI, is disabled until
support is completed.

NCQ and PCI MSI are disabled by default.  Marvell says "we use NCQ" in
their drivers but "we do not use PCI MSI."  Theoretically that implies
we need to fix ahci.c to work with Marvell NCQ, but one wonders why
Marvell NCQ is any different from other AHCI chips.

Signed-off-by: Jeff Garzik <jeff@garzik.org>