ARM: dts: at91: sama5d2: add nand0 and nfc0 nodes

Both nodes are required to access NAND Flash memory. Additional
settings will be necessary at the board level to use it.

Tested-by: Wenyou Yang <wenyou.yang@atmel.com>
Reviewed-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Romain Izard <romain.izard.pro@gmail.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>