net: dsa: microchip: move KSZ9477 and LAN937 ksz_dev_ops to individual drivers

The ksz_dev_ops() are specific to each switch family so they should
belong to the individual drivers instead of the common section.

Move the ksz_dev_ops() definitions of the KSZ9477 and the LAN937 to
their individual drivers.
Set static the functions that aren't exported anymore.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Bastien Curutchet (Schneider Electric) <bastien.curutchet@bootlin.com>
Link: https://patch.msgid.link/20260505-clean-ksz-driver-v1-4-05d70fa42461@bootlin.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>