ARM: NSP: add minimal Northstar Plus device tree

Add a very minimalistic set of Northstar Plus Device Tree files which
describes the SoC and the BCM958625 implementation.  The perpherials
described are:

ARM Cortex A9 CPU
2 8250 UARTs
ARM GIC
PL310 L2 Cache
ARM A9 Global timer

Signed-off-by: Kapil Hali <kapilh@broadcom.com>
Signed-off-by: Jon Mason <jonmason@broadcom.com>
Reviewed-by: Ray Jui <rjui@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>