net/mlx5: E-Switch, Introduce FDB hardware capabilities

Define needed hardware structures and capabilities needed
for E-Switch FDB flow tables and read them on driver load.

Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>