ep93xx: add dmaengine platform code

Add platform support code for the new EP93xx dmaengine driver.

Signed-off-by: Mika Westerberg <mika.westerberg@iki.fi>
Signed-off-by: Ryan Mallon <rmallon@gmail.com>
Acked-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>