ARM: dts: NSP: Add BCM958625K switch ports

Add the layout of the switch ports found on the BCM958625K reference
board. The CPU port is hooked up to the AMAC0 Ethernet controller
adapter.

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