ide: sanitize handling of IDE_HFLAG_NO_SET_MODE host flag

* Check for IDE_HFLAG_NO_SET_MODE host flag in ide_set_pio(),
  ide_set_[pio,dma]_mode(), ide_set_xfer_rate() and set_pio_mode().

* Remove no longer needed IDE_HFLAG_NO_SET_MODE host flag checking
  from ide_tune_dma().

* Remove superfluous ->set_pio_mode checking from do_special().

This is a part of preparations for adding 'struct ide_port_ops'.

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