libs: encoder: vp9: add low power mode encode
libs: encoder: vp9: add low power mode encode

By now, this feature only support by media-driver on Ice Lake
platform, more information you can reference:
https://github.com/intel/media-driver

GStreamer/gstreamer-vaapi,ceyusa/gstreamer-vaapi,ceyusa/gstreamer-vaapi,GStreamer/gstreamer-vaapi