Bluetooth: controller: Hide advance features in Kconfig

Added a explicit Kconfig option to show the Controller's
advanced feature configurations. These feature
configurations need specific in-depth Controller
implementation knowledge and should not overwhelm normal
users of the Controller.

Change-id: Iae764f2b266b199cf180936c51c7a4ea089ee510
Signed-off-by: Vinayak Chettimada <vinayak.kariappa.chettimada@nordicsemi.no>