Implement AHCI PMP support. ahci only supports command based
switching. Also, for some reason, NCQ over PMP doesn't work now.
Other than that, everything works.
Tested on ICH9R, JMB360/363 + SIMG3726, 4726 and 5744.
Signed-off-by: Tejun Heo <htejun@gmail.com>
Cc: Forrest Zhao <forrest.zhao@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>