net: dsa: microchip: move phylink_mac_ops to individual drivers

Similar to ksz_dev_ops, struct phylink_mac_ops shouldn't be part of
the common code. Instead, the common code should provide callable
functionality.

Invert the paradigm and export the common aspects from ksz_common.c, and
move the chip-specific stuff in individual drivers.

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-v1-5-05d70fa42461@bootlin.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>