OMAP2420: hwmod data: add system DMA

Add OMAP2420 DMA hwmod data and also add required
DMA device attributes.

Signed-off-by: G, Manjunath Kondaiah <manjugk@ti.com>
Acked-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>