dt-bindings: net: dsa: microchip: Add LAN9646 switch support

LAN9646 switch is a 6-port switch with functions like KSZ9897.  It has
4 internal PHYs and 1 SGMII port.

Signed-off-by: Tristram Ha <tristram.ha@microchip.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://patch.msgid.link/20241109015705.82685-2-Tristram.Ha@microchip.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>