net: dsa: microchip: Add LAN9646 switch support to KSZ DSA driver

LAN9646 switch is a 6-port switch with functions like KSZ9897.  It has
4 internal PHYs and 1 SGMII port.  The chip id read from hardware is
same as KSZ9477, so software driver needs to create a new chip id and
group allowable functions under its chip data structure to
differentiate the product.

Signed-off-by: Tristram Ha <tristram.ha@microchip.com>
Link: https://patch.msgid.link/20241109015705.82685-3-Tristram.Ha@microchip.com


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