ARM: dts: NSP: Add NAND Support to DT

Add NAND support to the device tree for the Broadcom Northstar Plus SoC.
Since no driver changes are needed to enable this hardware, only the
device tree changes are required to make this functional.

Signed-off-by: Jon Mason <jonmason@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>