net: dsa: ksz_common: provide own phylink MAC operations

Convert ksz_common to provide its own phylink MAC operations, thus
avoiding the shim layer in DSA's port.c

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Link: https://lore.kernel.org/r/E1s0O7H-009gpq-IF@rmk-PC.armlinux.org.uk


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