ARM: dts: r9a06g032: describe switch

Add description of the switch that is present on the RZ/N1 SoC. This
description includes ethernet-ports description for all the ports that
are present on the switch along with their connection to the MII
converter ports and to the GMAC for the CPU port.

Signed-off-by: Clément Léger <clement.leger@bootlin.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>