ide: remove ->ide_dma_on and ->dma_off_quietly methods from ide_hwif_t

* Make ide_dma_off_quietly() and __ide_dma_on() always available.

* Drop "__" prefix from __ide_dma_on().

* Check for presence of ->dma_host_on instead of ->ide_dma_on.

* Convert all users of ->ide_dma_on and ->dma_off_quietly methods
  to use ide_dma_on() and ide_dma_off_quietly() instead.

* Remove no longer needed ->ide_dma_on and ->dma_off_quietly methods
  from ide_hwif_t.

* Make ide_dma_on() void.

There should be no functionality changes caused by this patch.

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