package/qt5multimedia: put back gstreamer 0.10 optional dependency

Commit b2e16ea6 tried to remove
gstreamer 0.10 support by removing its dependency but this was just
masking the issue as we have a build failure with gstreamer 0.10

So put back this dependency.

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>