power: Always manage notify_on_migrate

Change-Id: I484b489dd0b71a7499d8f5d1a7ab0287d9af03f7
cmpower: Add support for set_interactive extension

 * Some devices might want to do custom stuff when the
   screen turns on/off. Add a hook for this.

Change-Id: If11fb34422bfcc776ae5ed48b43feb8468ca5d67