Bluetooth: Remove HCI prefix from SMP LTK defines

The LTK type has really nothing to do with HCI so it makes more sense to
have these in smp.h than hci.h. This patch moves the defines to smp.h
and removes the HCI_ prefix in the same go.

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