mmc: pxamci: switch over to dmaengine use

Switch over pxamci to dmaengine. This prepares the devicetree full
support of pxamci.

This was successfully tested on a PXA3xx board, as well as PXA27x.

Signed-off-by: Daniel Mack <zonque@gmail.com>
[adapted to pxa-dma]
Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>