tests: drivers: clock_control: nrf: Add suite for bluetooth API

Nordic platforms exposes API for controlling HF clock along
onoff API. This API is dedicated to be used by the bluetooth
controller and must not be used elsewhere.

Test suite is validating stability of HF clock control using
onoff API and specialized API.

Signed-off-by: Krzysztof Chruscinski <krzysztof.chruscinski@nordicsemi.no>