boards nrf5340bsim_cpuapp: Define chosen entropy source

Override the chosen entropy source irrespectively of what the
SOC may chose.
This is to avoid problems as the SOC may select the
cryptocell, but we do not support it in the simulated
target.

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

boards/posix/nrf_bsim/nrf5340bsim_nrf5340_cpuapp.dts

@@ -45,6 +45,7 @@
 	};
 
 	chosen {
+		zephyr,entropy = &rng_hci;
 		zephyr,flash = &flash0;
 		zephyr,bt-hci-ipc = &ipc0;
 		nordic,802154-spinel-ipc = &ipc0;