v4l2object: set colorspace for output devices
When the v4l2 device is an output device, the application shall set the colorspace. So map GStreamer colorimetry info to V4L2 colorspace and set on set_format. In case we have no colorimetry information, we try to guess it according to pixel format and video size. https://bugzilla.gnome.org/show_bug.cgi?id=737579