nrf5x_bsim: Add helper kconfig symbols for simulated nrf5340

Just like for the nrf52_bsim let's add helper kconfig symbols
which can be used to identify we are running in a target that
is compatible with the real HW but is not the real HW.

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