ide: remove CONFIG_IDEDMA_IVB config option

Devices which don't set word 93 validation bit should be now handled by
ide-iops.c::ivb_list[] and for debugging purposes cable detection can be
completely overriden with "idex=ata66" parameter.

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