gst1-imx: add package

Open-source GStreamer 1.0 plugins for i.MX6 platforms.
More info at https://github.com/Freescale/gstreamer-imx



[Peter: add upstream URL to help text]
Signed-off-by: Gary Bisson <bisson.gary@gmail.com>
Reviewed-by: Luca Ceresoli <luca@lucaceresoli.net>
Tested-by: Luca Ceresoli <luca@lucaceresoli.net>
Tested-by: Rostislav Lisovy <lisovy@jablotron.cz>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>