sama5d3/at91sam9: update the defconfig to include gst v4l2src plug-in

Use following command to preview ov2640 in lcd (take sama5d3 as example):
  gst-launch v4l2src device="/dev/video1" ! video/x-raw-yuv,width=640,height=480 ! ffmpegcolorspace ! fbdevsink

Signed-off-by: Josh Wu <josh.wu@atmel.com>