[PATCH] ahci: relocate several internal functions

* move ahci_port_start/stop() below EH functions.  This makes ahci
  more consistent with other drivers and makes prototypes for
  ahci_start/stop_engine() unnecessary.

* swap positions between ahci_start_engine() and ahci_stop_engine()
  for readability.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Zhao, Forrest <forrest.zhao@intel.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>