channel-display-gst: Prefer playbin3 to playbin

If playbin3 is available (checked in Gstreamer registry), it
makes sense to prefer it given the major improvements and
features it offers including the capability to handle higher
bitrates.

Cc: Frediano Ziglio <freddy77@gmail.com>
Cc: Dongwon Kim <dongwon.kim@intel.com>
Cc: Hazwan Arif Mazlan <hazwan.arif.mazlan@intel.com>
Signed-off-by: Jin Chung Teng <jin.chung.teng@intel.com>
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
Acked-by: Frediano Ziglio <freddy77@gmail.com>