net: dsa: microchip: update fdb add/del/dump in ksz_common

This patch makes the dsa_switch_hook for fdbs to use ksz_common.c file.
And from ksz_common, individual switches fdb functions are called using
the dev->dev_ops. And removed the r_dyn_mac_table, r_sta_mac_table and
w_sta_mac_table from ksz_dev_ops as it is used only in ksz8795.c

Signed-off-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>