mlxsw: core: Register devlink instance before sub-objects

Recent changes made it possible to register the devlink instance before
its sub-objects and under the instance lock. Among other things, it
allows us to avoid warnings such as this one [1]. The warning is
generated because a buggy firmware is generating a health event during
driver initialization, before the devlink instance is registered.

Move the registration of the devlink instance to the beginning of the
initialization flow to avoid such problems.

A similar change was implemented in netdevsim in commit 82a3aef2
("netdevsim: move devlink registration under the instance lock").

[1]
WARNING: CPU: 3 PID: 49 at net/devlink/leftover.c:7509 devlink_recover_notify.constprop.0+0xaf/0xc0
[...]
Call Trace:
 <TASK>
 devlink_health_report+0x45/0x1d0
 mlxsw_core_health_event_work+0x24/0x30 [mlxsw_core]
 process_one_work+0x1db/0x390
 worker_thread+0x49/0x3b0
 kthread+0xe5/0x110
 ret_from_fork+0x1f/0x30
 </TASK>

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>