ide: ->ide_dma_clear_irq() -> ->clear_irq()

* Rename ->ide_dma_clear_irq method to ->clear_irq
  and move it from ide_hwif_t to struct ide_port_ops.

* Move ->waiting_for_dma check inside ->clear_irq method.

* Move ->dma_base check inside ->clear_irq method.

piix.c:
* Add ich_port_ops and remove init_hwif_ich() wrapper.

There should be no functional changes caused by this patch.

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