[CFT 04/11] mmc: omap: add DMA engine support

* Russell King [off-list ref] [120607 04:11]:

Add DMA engine support to the OMAP driver.  This supplements the
private DMA API implementation contained within this driver, and the
driver can be switched at build time between using DMA engine and the
private DMA API.

Signed-off-by: Russell King <redacted>

This I boot tested on 770 and N800:

Tested-by: Tony Lindgren <tony@atomide.com>