sl82c105: DMA support code cleanup (take 4)

Fold the now equivalent code in the ide_dma_check() method into a mere call to
ide_use_dma().  Make config_for_dma() return non-zero if DMA mode has been set
and call it from the ide_dma_check() method instead of ide_dma_on().
Defer writing the DMA timings to the chip registers until DMA is really turned
on (and do not enable IORDY for DMA).
Remove unneeded code from the init_hwif() method, improve its overall looks.
Rename the dma_start(), ide_dma_check(), and ide_dma_lostirq() methods, and
also use more proper hwif->dma_command, fix printk() and comment in the latter
one as well.  While at it, cleanup style in several places.

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