net: dsa: Add support for devlink resources

Add wrappers around the devlink resource API, so that DSA drivers can
register and unregister devlink resources.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>