ide: remove ide_dma_enable()

* check ->speedproc return value in ide_tune_dma()
* use ide_tune_dma() in cmd64x/cs5530/sc1200/siimage/sl82c105/scc_pata drivers
* remove no longer needed ide_dma_enable()

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