vaapipostproc: add support for DMABuf caps feature
vaapipostproc: add support for DMABuf caps feature

https://bugzilla.gnome.org/show_bug.cgi?id=755072

Signed-off-by: Julien Isorce <2904e845d63d102574cbb95a4bcdefac0a5d7af0@samsung.com>

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