Bluetooth: Notify about device registration before power on

It is important that the monitor interface gets notified about
a new device before its power on procedure has been started.

For some reason that is no longer working as expected and the power
on procedure runs first. It is safe to just notify about device
registration and trigger the power on procedure afterwards.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Acked-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>