ide: add ide_dev_has_iordy() helper (take 4)

* Add ide_dev_has_iordy() helper and use it sl82c105 host driver.

* Remove no longer needed ide_pio_data_t.use_iordy field.

v2/v3:
* Fix issues noticed by Sergei:
  - correct patch description
  - fix comment in ide_get_best_pio_mode()

v4:
* 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>