driver core: bus: bus_register/unregister_notifier() cleanups

Convert the bus_register_notifier() and bus_unregister_notifier() public
functions to use bus_to_subsys() and not use the back-pointer to the
private structure as well as the bus_notify() function.

Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Link: https://lore.kernel.org/r/20230208111330.439504-11-gregkh@linuxfoundation.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>