Bluetooth: Add AES crypto context for each HCI device

Previously the crypto context has only been available for LE SMP
sessions, but now that we'll need to perform operations also during
discovery it makes sense to have this context part of the hci_dev
struct. Later, the context can be removed from the SMP context.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>