cmd640: always auto-tune PIO

* Default to tuning PIO0 and disabling prefetch prior to probing
  devices for CONFIG_BLK_DEV_CMD640_ENHANCED=y case.

* Always auto-tune PIO.

* Remove no longer used retrieve_drive_counts().

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
1 file changed