Remove atapi_ireason_t.

While at it:
* replace 'HWIF(drive)' by 'drive->hwif' (or just 'hwif' where possible)

v2:
* v1 had CD and IO bits reversed in many places.

* Use CD and IO defines from <linux/hdreg.h>.

v3:
* Fix incorrect "(ireason & IO) == test_bit()". (Noticed by Sergei)
Acked-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>