fsl_dma: Make DMA transactions snoopable

Make DMA transactions snoopable so that CPUs can keep caches up-to-date.
This allows dma transactions to be used for operations such as memory
copies without any additional cache control operations.

Signed-off-by: Peter Tyser <ptyser@xes-inc.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>