package/qt5/qt5multimedia: fix gstreamer1 support

Fix the missing gstreamer1 build dependencies, which could possibly
prevent the configuration of qt5multimedia from detecting the supported
gstreamer1 features.

Fix the missing gstreamer1 install rules, which resulted in the
following runtime error:

    defaultServiceProvider::requestService(): no service found for - "org.qt-project.qt.mediaplayer"

Signed-off-by: Benoît Thébaudeau <benoit@wsystem.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>