ahci,ata_generic: let ata_generic handle new MBP w/ MCP89

For yet unknown reason, MCP89 on MBP 7,1 doesn't work w/ ahci under
linux but the controller doesn't require explicit mode setting and
works fine with ata_generic.  Make ahci ignore the controller on MBP
7,1 and let ata_generic take it for now.

Reported in bko#15923.

  https://bugzilla.kernel.org/show_bug.cgi?id=15923

NVIDIA is investigating why ahci mode doesn't work.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Peer Chen <pchen@nvidia.com>
Cc: stable@kernel.org
Reported-by: Anders Østhus <grapz666@gmail.com>
Reported-by: Andreas Graf <andreas_graf@csgraf.de>
Reported-by: Benoit Gschwind <gschwind@gnu-log.net>
Reported-by: Damien Cassou <damien.cassou@gmail.com>
Reported-by:  <tixetsal@juno.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>