dt-bindings: net: dsa: document additional Microchip KSZ8563 switch

It is a 3-Port 10/100 Ethernet Switch with 1588v2 PTP.

Signed-off-by: Razvan Stefanescu <razvan.stefanescu@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>