boards: nrf_bsim: Add new nrf5340 board definitions

With the proper structure for the hwmv2, and matching the
real HW ones.
Also add a note about the old ones being just a middle step
for backwards compatibility.

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>

boards/native/nrf_bsim/Kconfig.nrf5340bsim

@@ -0,0 +1,5 @@
+# Copyright (c) 2024 Nordic Semiconductor ASA
+# SPDX-License-Identifier: Apache-2.0
+
+config BOARD_NRF5340BSIM
+	select SOC_POSIX

boards/native/nrf_bsim/board.yml

@@ -3,6 +3,16 @@ boards:
   vendor: Zephyr
   socs:
   - name: native
+- name: nrf5340bsim
+  vendor: Zephyr
+  socs:
+  # Note this is referring to the real SOC yaml, but we only use its name and cpu-cluster definition
+  # In practice this board uses the same native SOC (SOC_POSIX) as the nrf52_bsim
+  - name: nrf5340
+
+# These two board definitions below, together with their respective
+# Kconfig.nrf5340bsim_nrf5340_cpu[app,net] exist for backwards compatibility with hwmv1 usage
+# Once all their usage in tree is removed, or aliases have been introduced they can be removed.
 - name: nrf5340bsim_nrf5340_cpuapp
   vendor: Zephyr
   socs: