devlink: Simplify internal devlink params implementation

Reduce extra indirection from devlink_params_*() API. Such change
makes it clear that we can drop devlink->lock from these flows, because
everything is executed when the devlink is not registered yet.

Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>