ata: add ata_id_pio_need_iordy() helper (v2)

v2:
Minor fixes per Sergei's review.

Cc: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Cc: Jeff Garzik <jgarzik@pobox.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>