ARM: dts: atlas7: put pinctl property to get pinmux for NAND

Nand controller often share some pins with sd/mmc controller on
atlas and prima series, nand node can be disabled if the pins are
used by sd/mmc controller.

Signed-off-by: Huayi Li <huayi.li@csr.com>
Signed-off-by: Barry Song <Baohua.Song@csr.com>