Bluetooth: Controller: re-add missing hci_vendor.c reference

Move the nordic and openisa vendor file under ll_sw and add them back to
the list when building for nRF platforms, this was inadvertently removed
in

7bd2804c Bluetooth: Controller: Build vendor LLL as library

and is currently causing a:

<wrn> bt_id: No static addresses stored in controller

and random address on nRF devices.

Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>
Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>