DMAENGINE: add runtime slave control to COH 901 318 v3

This extends the DMA engine driver for the COH 901 318 used in the
U300 platform with the generic runtime slave control command.

Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>