ide: (hopefully) fix VDMA for CS5520

* Set the correct hwif->dma_base for the second channel in
  ide_get_or_set_dma_base().

* Remove DMA enable code from cs5520_set_pio_mode(), this can
  be handled by the generic ->dma_host_on method now.

* Add VDMA check to ide_config_drive_speed().

* drive->using_dma was never enabled since cs5520 host driver's
  ->ide_dma_on method overrided the generic ->ide_dma_on (so
  __ide_dma_on() was never called, drive->using_dma was never set
  and VDMA was never used since it depends on drive->using_dma).

  Fix it by using ->dma_host_on method instead of ->ide_dma_on
  (also add matching ->dma_host_off method).

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