palm_bk3710: use ->init_dma method

* Move DMA setup to palm_bk3710_init_dma().

* Convert the driver to use ->init_dma method.

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