Switch from native_posix to native_sim as default test platform
And switch overlays to native_sim.
Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>
The system still takes both prefixed and unprefixed dt-bindings files,
but let's use zephyr/ prefixed in the examples and documentation.
Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>