sl82c105: add speedproc() method and MWDMA0/1 support

Add the speedproc() method for setting transfer modes, modify config_for_dma()
to call it and use ide_max_dma_mode() to select the best DMA mode.
Add support for the multiword DMA modes 0 and 1, using the upper half of the
'drive_data' field to store the DMA timings to program into the drive control
register when DMA is turned on for real.

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>