Support Nvidia proprietary driver when using NVreg_PreserveVideoMemoryAllocations

Currently the script isn't able to run on systems with Nvidia card due to being unable to enter sleep mode, even though Nvidia has a S0ix config.

Apparently the script tries to sleep by writing to `/sys/power/state` but this won't work on Nvidia when you use `NVreg_PreserveVideoMemoryAllocations`, since that requires starting the sleep via systemd, which is the default in RPMFusion's version of the Nvidia driver.

Please see https://us.download.nvidia.com/XFree86/Linux-x86_64/525.89.02/README/powermanagement.html

Error:

```
The system failed to place S2idle entry command by turbostat,
please check if the suspend is failed or turbostat tool version is old
e.g. did you make turbostat tool executable or separately run S2idle command:
rtcwake -m freeze -s 15
```