serverworks: PIO mode setup fixes

* limit max PIO mode to PIO4, this driver doesn't support PIO5 and attempt
  to program PIO5 by svwks_tune_chipset() could result in incorrect PIO
  timings being programmed and possibly the data corruption (it seems that
  the minimum possible values were used but I lack the datasheets to be sure)

* select best PIO mode in svwks_tune_drive() and not in svwks_tune_chipset()
  when doing PIO autotuning (pio == 255)

* don't try to tune PIO in config_chipset_for_dma() as ide_dma_enable() could
  return 1 if DMA was previously enabled (svwks_config_drive_xfer_rate()
  takes care of PIO tuning if no suitable DMA mode is found)

* remove config_chipset_for_pio() and use svwks_tune_drive() instead,
  config_chipset_for_pio() contained numerous bugs when selecting PIO mode
  (luckily it was only used for devices limited to PIO by capabilities/BIOS):

  - it didn't check for validity of id->eide_pio_modes and id->eide_pio_iordy
    before using them

  - it tried to found out maximum PIO mode basing on minimum IORDY cycle time
    (moreover wrong cycle times were used for PIO0/1/5)

  - it was overriding PIO blacklist and conservative PIO "downgrade" done
    by ide_get_best_pio_mode()

  - if the max drive PIO was PIO5 then XFER_PIO_0/XFER_PIO_SLOW was selected
    (XFER_PIO_SLOW is not supported by svwks_tune_chipset() so the result
     was the same as if using XFER_PIO_5 => wrong PIO timings were set)

  - it was overriding drive->current_speed

* bump driver version

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