net: devlink: remove region snapshot ID tracking dependency on devlink->lock

After mlx4 driver is converted to do locked reload, functions to get/put
regions snapshot ID may be called from both locked and unlocked context.

So resolve this by removing dependency on devlink->lock for region
snapshot ID tracking by using internal xa_lock() to maintain
shapshot_ids xa_array consistency.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>