Remove "P2 forced" state from drivers

[wpierce]

This is fixed on the latest R580 and all future branches:

What's the situation with vdpau/vaapi/nvdec?

This is fixed on the latest R580 and all future branches with the use of the CUDA_DISABLE_PERF_BOOST environment variable. Added a new environment variable, CUDA_DISABLE_PERF_BOOST, to allow for disabling the default behavior of boosting the GPU to a higher power state when running CUDA applications. Setting this environment variable to ‘1’ will disable the boost.