soc inf (native): Refactor into a top and bottom

Where the bottom is the only one which interacts with
the host operating system.
And the top the only one that interacts or is aware
of the hosted operating system (Zephyr).

The bottom uses the native simulator CPU
start/stop emulation.
By now we replicate its code as a provisional measure,
until the native simulator becomes standard.

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