devlink: introduce couple of dumpit callbacks for split ops

Introduce couple of dumpit callbacks for generated split ops. Have them
as a thin wrapper around iteration function and allow to pass dump_one()
function pointer directly without need to store in devlink_cmd structs.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Link: https://lore.kernel.org/r/20230803111340.1074067-8-jiri@resnulli.us


Signed-off-by: Jakub Kicinski <kuba@kernel.org>