Bluetooth: le_simult_central_peripheral experimental feature

This patch adds an le_simult_central_peripheral features which allows a
clients to determine if the controller is able to support peripheral and
central connections separately and at the same time.

Signed-off-by: Alain Michaud <alainm@chromium.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>