Bluetooth: Add initial code for distributing local IRK

This code adds a HCI_PRIVACY flag to track whether Privacy support is
enabled (meaning we have a local IRK) and makes sure the IRK is
distributed during SMP key distribution in case this flag is set.

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