net: lan966x: add mactable support

This patch adds support for MAC table operations like add and forget.
Also add the functionality to read the MAC address from DT, if there is
no MAC set in DT it would use a random one.

Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>