Bluetooth: host: GATT Lazyloading cleanup at disconnect

Mark the ram version of the ccc_cfg as free after ccc has been
stored when a bonded device disconnects.
If the device use lazy loading of settings then ccc_cfg was not
cleaned up properly when a bonded device disconnects. This
resulted in the ccc system ran out of ccc_cfg resources after
having disconnected CONFIG_BT_MAX_CONN times.

Signed-off-by: Kim Sekkelund <ksek@oticon.com>