devlink: move devlink_notify_register/unregister() to dev.c

At last, move the last bits out of leftover.c,
the devlink_notify_register/unregister() functions to dev.c

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Link: https://lore.kernel.org/r/20230828061657.300667-16-jiri@resnulli.us


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