Preceding xfer_mask changes make the following functions unused.

  ata_pio_modes(), base_from_shift(), ata_pr_blacklisted(), fgb()

Kill them.  Also, as xfer_mode_str[] is now only used by
ata_mode_string(), move it into the function.
Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>