Bluetooth: Add MGMT handlers for dealing with SMP LTK's

This adds a method to notify that a new LTK is available and
a handler to store keys coming from userspace into the kernel LTK
list.

Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@openbossa.org>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>