net/mlx4: Use devl_ API for devlink region create / destroy

Use devl_ API to call devl_region_create() and devl_region_destroy()
instead of devlink_region_create() and devlink_region_destroy().
Add devlink instance lock in mlx4 driver paths to these functions.

This will be used by the downstream patch to invoke mlx4 devlink reload
callbacks with devlink lock held.

Signed-off-by: Moshe Shemesh <moshe@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>