ARM: dts: vf610: Add ZII SSMB DTU board

Add the Zodiac Digital Tapping Unit, a VF610 based network device with
5 Ethernet ports. One of these ports supports 1000Base-T2.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>