mmc: mmci: do an EOT for write DMA requests.

This patch adds an hack to get the BAM working. In general generic
drivers are not allowed to call SOC specific functions, but as this is
just an hack for demo.

Currently, Andy Gross is looking at, how to expose this function in more
generic way.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>