fix csi clko2 clock handling
- clko2 should be handled by the NXP mipi. But that isn't needed for "just turning on" a camera. Since we currently want the sensor runtime_pm to fully turn on/off, we handle clko2 in those drivers too. This is mostly fine during runtime, but at least not a very clean solution. (and when doing system suspend, an already unprepared clock tries to get unprepared again, which leads to warnings).
- related is #252 when drivers probe without powered cameras
- A longer term "solution" can be to make only mipi handle clko2 and test cameras only by recording frames.