Instead of using gst_video_info_to_caps () to generated the fixed src caps,
this patch enables the first step for caps negotiation with a possible
following caps filter.
_get_preferred_caps() will traverse the possible src caps looking for the one
wit the preferred feature and the preferred color format. Then the color
format, the frame size and the frame rate are fixated.
https://bugzilla.gnome.org/show_bug.cgi?id=758548
When running transform_caps() vmethod, returning the srcpad caps, the caps are
early restricted to the element properties set: width, height, format and
force keep aspect.
A new file was added gstvaapipostprocutil.{c,h} where the utilities functions
are stored.
https://bugzilla.gnome.org/show_bug.cgi?id=758548
