dma: coh901318: push platform data into driver

We're only ever going to support the U300 with this driver
so skip the separation of platform data from driver, and push
it down into the driver itself.

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