omxvideoenc: ensure enough buffers are allocated in the pool
omxvideoenc: ensure enough buffers are allocated in the pool

Handle allocation query and ensure enough buffers are allocated in
the negotiated pool. This help preventing buffer starvation in the pipeline.

https://bugzilla.gnome.org/show_bug.cgi?id=785122

GStreamer/gst-omx,GStreamer/gst-omx,GStreamer/gst-omx,CapOM/gst-omx,CapOM/gst-omx,CapOM/gst-omx