* Move xfer mode tuning code to ide-xfer-mode.c.

* Add CONFIG_IDE_XFER_MODE config option to be selected by host drivers
  that support xfer mode tuning.

* Add CONFIG_IDE_XFER_MODE=n static inline versions of ide_set_pio()
  and ide_set_xfer_rate().

* Make IDE_TIMINGS and BLK_DEV_IDEDMA config options select IDE_XFER_MODE,
  also add explicit selects for few host drivers that need it.

* Build/link ide-xfer-mode.o and ide-pio-blacklist.o (it is needed only
  by ide-xfer-mode.o) only if CONFIG_IDE_XFER_MODE=y.

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