fsldma: fix issue of slow dma

Fixed fsl dma slow issue by initializing dma mode register with
bandwidth control. It boosts dma performance and should works
with 85xx board.

Signed-off-by: Forrest Shi <b29237@freescale.com>
Signed-off-by: Li Yang <leoli@freescale.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>