eeprom sim: Enhance & refactor native part so it works w emb libCs

For the parts of the simulator which are dedicated for the native
platforms (POSIX arch based):
* Refactor the parts that interacts with the host, so it is possible to
  use it also with embedded libCs
* Enhance it with more options to allow:
  * Keeping the content just in RAM
  * Erasing the EEPROM file at exit
  * Clearing the file at boot
* Also show in the command line help the default file name.

As part of this:

* Update the kconfig dependencies, so we allow building it with other
  C libraries in the native targets
* Update the table in the native_sim docs to indicate all C libraries
  are supproted now

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