gupnp-dlna: Update to 0.9.4, support gstreamer

Minor update.
As we now have GStreamer 1.0+, add a PACKAGECONFIG option
to build the additional "gupnp-dlna-gst" library if it is
present.
This is most notably needed by Rygel.

Signed-off-by: Manuel Bachmann <manuel.bachmann@iot.bzh>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>