ARM: davinci: dm646x: Add dma_slave_map to edma

Provide the dma_slave_map to edma which will allow us to move the drivers
to the new, simpler dmaengine API and we can remove the DMA resources also
for the devices.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
[nsekhar@ti.com: fix typos in code]
Signed-off-by: Sekhar Nori <nsekhar@ti.com>