ide: add ide_pio_cycle_time() helper (take 2)

ide: add ide_pio_cycle_time() helper (take 2)

* Add ide_pio_cycle_time() helper.

* Use it in ali14xx/ht6560b/qd65xx/cmd64{0,x}/sl82c105 and pmac host drivers
  (previously cycle time given by the device was only used for "pio" == 255).

* Remove no longer needed ide_pio_data_t.cycle_time field.

v2:
* Fix "ata_" prefix (Noticed by Jeff).

Acked-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Cc: Jeff Garzik <jeff@garzik.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>