gstreamer1.0-plugins-base: Fix output buffer can't writable after frame_map() issue

gstreamer1.0-plugins-base: Fix output buffer can't writable after frame_map() issue

-Add GST_VIDEO_FRAME_MAP_FLAG_NO_REF
 This makes sure that the buffer is not reffed another time when
 storing it in the GstVideoFrame, keeping it writable if it was writable.

-Use new GST_VIDEO_FRAME_MAP_FLAG_NO_REF to replace the old one because it's kind of ugly.

-Don't ref buffers twice when mapping

Signed-off-by: Yuqing Zhu <b54851@freescale.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>