mtd: atmel_nand: Add DMA support to access Nandflash

Some SAM9 chips have the ability to perform DMA between CPU and SMC controller.
This patch adds DMA support for SAM9RL, SAM9G45, SSAM9G46,AM9M10, SAM9M11.

Signed-off-by: Hong Xu <hong.xu@atmel.com>
Tested-by: Ryan Mallon <ryan@bluewatersys.com>
Acked-by: Ryan Mallon <ryan@bluewatersys.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>