ide: remove ide_use_fast_pio()

Remove ide_use_fast_pio() and just re-tune PIO unconditionally if DMA tuning
has failed in ->ide_dma_check.  All host drivers using ide_use_fast_pio() set
drive->autotune so PIO is always tuned anyway and in some cases we _really_
need to re-tune PIO because PIO and DMA timings are shared.

Acked-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>