DMAENGINE: COH 901 318 configure channel direction

This makes the COH 901 318 configure channel direction (to or from
device) dynamically, instead of being passed in from the platform
data. This was necessary in order to get the MMC/SD-card channel
bidirectional (all other channels on the U300 were either RX or
TX but this one was both). This also sets memcpy() alignent to
even 2^2 (32bit) boundaries, which makes the memcpy() stress tests
start working.

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