mac802154: cfg: add suspend and resume callbacks

This patch introduces suspend and resume callbacks to mac802154. When
doing suspend we calling the stop driver callback which should stop the
receiving of frames. A transceiver should go into low-power mode then.
Calling resume will call the start driver callback, which starts receiving
again and allow to transmit frames.

This was tested only with the fakelb driver and a qemu vm by doing the
following commands:

echo "devices" > /sys/power/pm_test
echo "freeze" > /sys/power/state

while doing some high traffic between two fakelb phys.

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>