[PATCH] libata: convert pio_task and packet_task to port_task

Make pio_task and atapi_packet_task use port_task.
atapi_packet_task() is moved upward such that it's right after
ata_pio_task().  This position is more natural and makes adding
prototype for ata_qc_issue_prot() unnecessary.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>