Horkage handling had the following problems.

* dev->horkage was positioned after ATA_DEVICE_CLEAR_OFFSET, so it was
  cleared before the device is configured.  This broke
  HORKAGE_DIAGNOSTIC.

* Some used dev->horkage while others called ata_device_blacklisted()
  directly.  This was at best confusing.

This patch moves dev->horkage right after dev->flags and set the field
according to the blacklist during device configuration.  All users
test against dev->horkage.  ata_device_blacklisted() now has only one
user, make it static.  While at it, rename it to ata_dev_blacklisted()
for consistency.
Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>