sata_mv:  Fix broken Marvell 7042 support.

The Marvell 7042 chip is more or less the same as the 6042 internally,
but sports a PCIe bus.  Despite having identical SATA cores, the 7042
does differ from its PCI bus counterparts in placment and layout of
certain bus related registers.

This patch fixes sata_mv to distinguish between the PCI bus registers
of earlier chips, and the PCIe bus registers of the 7042.

Specifically, move the offsets and bit patterns for the
PCI/PCIe interrupt cause/mask registers into the struct mv_host_priv,
as these values differ between the 6xxx and 7xxx series chips.

This fixes the driver to not access reserved PCI addresses,
and prevents the lockups reported in linux-2.6.24 with 7042 boards.

Also add a new PCI ID for the Highpoint 2300 7042-based board
that I'm using for testing this stuff here.

Tested with Marvell 6081 + 7042 chips, on x86 & x86_64.
Signed-off-by: Mark Lord <mlord@pobox.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>