Bluetooth: Make mgmt power down notification for BR/EDR explicit

The management interface only operates on BR/EDR controllers. The check
for the power down notification is a bit intermixed with the check if
controller auto power off is active. Since there are more than just
BR/EDR controllers supported, make this check explicit since the auto
power off check also applies to AMP controllers and it has to happen
in this exact order. Otherwise the bit will not be cleared.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>