vaapiencode: use pad query vmethods
vaapiencode: use pad query vmethods

GstVideoEncoder, the base class of vaapiencode, added support for pad queries
as virtual methods since gstreamer 1.4. This patch enables those vmethods,
while keeps support for previous versions of gstreamer.

This patch is relevant since GstVideoEncoder takes care of other queries that
we are currently ignoring.

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

https://bugzilla.gnome.org/show_bug.cgi?id=757629

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