libs: encoder: h265: support ICQ/QVBR BRC
libs: encoder: h265: support ICQ/QVBR BRC

Enable support for ICQ and QVBR bitrate control.

The code is essentially the same for h264 ICQ/QVBR support
which was added in commit 9e0c133a2403.

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