ASoC: add DMA platform driver for MX1x and MX2x

This adds support for DMA platform valid for i.MX1 and i.MX2 platforms.

This is not valid for i.MX3 since it doesn't share the same DMA
interface than i.MX1 and i.MX2.

It has been tested on i.MX27 board.

Signed-off-by: Javier Martin <javier.martin@vista-silicon.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>