nrf52_bsim: Convert to use the native simulator

Convert the nrf52_bsim board, to use the native simulator
as its engine.
This means some of the functionality the board included
before is now handled by the native simulator, including
the overall program main and CPU/HW scheduling.

Note that this board remains separate from the native_sim
board, even if both use the native simulator.

Also update the nRF HW models component to a new version
which has been converted into an extension for the
native simulator.

After this change, it becames also possible to build
the nrf52_bsim with an embedded C library, and to
use with it the Zephyr POSIX API shim.

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