dt-bindings: net: lan966x: Add additional properties for lan966x

This patch updates the dt-bindings for lan966x switch.
It adds the properties 'additionalProperties' and
'unevaluatedProperties' for ethernet-ports and ports nodes. In this way
it is not possible to add more properties to these nodes.

Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>