Expose LE Encrypt helpers to applications. If software-
based controller is compiled-in, then controller's AES
hardware will be used by the exposed helper interface.
Change-id: I2bac9dfa5ccb3dd50447079affb52d920ae5bd81
Signed-off-by: Vinayak Chettimada <vinayak.kariappa.chettimada@nordicsemi.no>.