mlxsw: resources: Add max cpu policers resource

Add a new resource to resources query: max cpu policers which tells us how
many policers can be used to limit the data rate to the cpu port.

Signed-off-by: Nogah Frankel <nogahf@mellanox.com>
Reviewed-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>