encoder: Only support YUV420 native format as input for now
encoder: Only support YUV420 native format as input for now

Practically we should be able to support more formats, for eg:
JPEG Encoder can support YUV422, RGBA and all.
But this is causing more issues which need proper fix here and there.

01org/iotg-lin-gfx-gstreamer-vaapi,GStreamer/gstreamer-vaapi,gbeauchesne/gstreamer-vaapi,gbeauchesne/gstreamer-vaapi,gbeauchesne/gstreamer-vaapi,CapOM/gstreamer-vaapi,01org/iotg-lin-gfx-gstreamer-vaapi,GStreamer/gstreamer-vaapi,CapOM/gstreamer-vaapi,CapOM/gstreamer-vaapi,ceyusa/gstreamer-vaapi,ceyusa/gstreamer-vaapi,01org/iotg-lin-gfx-gstreamer-vaapi