dma: coh901318: create a proper platform data file

This extracts the platform data that we will keep generic
from the U300 platform and associates it with the COH901318
driver in <linux/platform_data/dma-coh901318.h>.

Acked-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>