vaapipostproc: add support for crop regions in VPP mode.
vaapipostproc: add support for crop regions in VPP mode.

Apply video cropping regions stored in GstVideoCropMeta, or in older
GstVaapiSurfaceProxy representation, to VPP pipelines. In non-VPP modes,
the crop meta are already propagated to the output buffers.

https://bugzilla.gnome.org/show_bug.cgi?id=720730

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