FEI: Add support for FEI conditional build
FEI: Add support for FEI conditional build

FEI(Flexible Encoding Infrastructure) is an extension
to VA API. Define USE_H264_FEI_ENCODER based on
fei header file and required structures availability.

https://bugzilla.gnome.org/show_bug.cgi?id=785712
https://bugzilla.gnome.org/show_bug.cgi?id=784667

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