mtd: atmel_nand: add a new dt binding item for nand dma support

This patch will set the nand dma support in dts. Since we will not use
cpu_is_xxx() in nand driver. We needn't include the mach/cpu.h any more.

Signed-off-by: Josh Wu <josh.wu@atmel.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>