vaapidecodebin: delay the bin configuration
vaapidecodebin: delay the bin configuration

Delay the bin configuration until changing to READY state. This is because we
should add the vaapipostproc element until the vaapidecode has emitted the
HAVE_CONTEXT message, so de gst_bin_add() could set the context set to
vaapipostproc.

Signed-off-by: Víctor Manuel Jáquez Leal <victorx.jaquez@intel.com>

https://bugzilla.gnome.org/show_bug.cgi?id=757957

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