Bluetooth: Add mgmt suspend and resume events

Add the controller suspend and resume events, which will signal when
Bluetooth has completed preparing for suspend and when it's ready for
resume.

Signed-off-by: Abhishek Pandit-Subedi <abhishekpandit@chromium.org>
Reviewed-by: Miao-chen Chou <mcchou@chromium.org>
Reviewed-by: Sonny Sasaka <sonnysasaka@chromium.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>