dt-bindings: net: dsa: Add KSZ8567 switch support

This commit adds the dt-binding for KSZ8567, a robust 7-port
Ethernet switch. The KSZ8567 features two RGMII/MII/RMII interfaces,
each capable of gigabit speeds, complemented by five 10/100 Mbps
MAC/PHYs.

This binding is necessary to set specific capabilities for this switch
chip that are necessary due to the ksz dsa driver only accepting
specific chip ids.
The KSZ8567 is very similar to KSZ9567 however only containing 100 Mbps
phys on its downstream ports.

Signed-off-by: Philippe Schenker <philippe.schenker@impulsing.ch>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Link: https://lore.kernel.org/r/20240130083419.135763-1-dev@pschenker.ch
Signed-off-by: Paolo Abeni <pabeni@redhat.com>