net: ethernet: ti: ale: add cpsw_ale_get_num_entries api

Add cpsw_ale_get_num_entries() API to return number of ALE table entries
and update existing drivers to use it.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>