libs: encoder: Add properties for vp9 encoder.
libs: encoder: Add properties for vp9 encoder.

Install properties for vp9 encoder class. Also set the new get/set
property functions for gobject class. Still use the old properties
way now and this new feature will be enabled later.

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