drivers: net: cpsw: add support to dump ALE table via ethtool register dump

Add support to view addresses added by the driver and learnt by the
hardware from ALE table via ethtool register dump interface.

Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>