Adds native_posix hw counter model and the counter driver.
Functionality is needed by software which is tested
on native_posix and has dependency on counter.
Hardware model was developed similarly to HW timer model.
The counter driver wraps HW counter functions and exposes
basic functionalities: starting, stopping, setting and cancelling
single channel alarms.
Code was tested against: tests/drivers/counter/counter_basic_api.
Signed-off-by: Filip Zajdel <filip.zajdel@nordicsemi.no>
