gstgldisplay: no need the I420 work around if ATI Mobility
gstgldisplay: no need the I420 work around if ATI Mobility

fix #588653

mapmapteam/gst-plugins-gl,ystreet/gst-plugins-gl,ystreet/gst-plugins-gl,mapmapteam/gst-plugins-gl,ystreet/gst-plugins-gl,mapmapteam/gst-plugins-gl