net: marvell: prestera: do not propagate netdev events to prestera_switchdev.c

Replace prestera_bridge_port_event(...) by
prestera_bridge_port_join(...) and prestera_bridge_port_leave().

It simplifies the code by reading netdev event specific handling only
once in prestera_main.c

Signed-off-by: Vadym Kochan <vkochan@marvell.com>
CC: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>