atiixp: remove ->dma_host_on and ->dma_host_off methods

* Enable/disable UDMA in atiixp_set_dma_mode().

* Remove no longer needed atiixp_dma_host_{on,off}() and save_mdma_mode[].

* Bump driver version.

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