[libata] sata_nv: add SW NCQ support for MCP51/MCP55/MCP61

Add the Software NCQ support to sata_nv.c for MCP51/MCP55/MCP61 SATA
controller.  NCQ function is disable by default, you can enable it
with 'swncq=1'.  NCQ will be turned off if the drive is Maxtor on
MCP51 or MCP55 rev 0xa2 platform.

[akpm@linux-foundation.org: build fix]
Signed-off-by: Kuan Luo <kluo@nvidia.com>
Signed-off-by: Peer Chen <pchen@nvidia.com>
Cc: Zoltan Boszormenyi <zboszor@dunaweb.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>