PCM sensor server: configurable collection time

Would love the ability to configure the timer resolution for the PCM sensor server, so I can get more precise measurements. Currently it refreshes every second, according to [this line](https://github.com/intel/pcm/blob/master/src/pcm-sensor-server.cpp#L2777):

```cpp
now = now + std::chrono::seconds(1);
std::this_thread::sleep_until( now );
```