VxWorks: Enable video device discovery

Video devices should be discovered by VxWorks properly.

Pick-to: 6.8
Task-number: QTBUG-115777
Change-Id: Ib6719fc9480827aed296343e0b91286ae8408c8a
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>
(cherry picked from commit fbd7c7c45af8102090cf9e606ade565e5357a220)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/platformsupport/devicediscovery/qdevicediscovery_vxworks.cpp

@@ -47,6 +47,10 @@ QStringList QDeviceDiscoveryVxWorks::scanConnectedDevices()
         }
     }
 
+    if (m_types & Device_VideoMask) {
+        devices << QString::fromLatin1("/dev/dri/card0");
+    }
+
     return devices;
 }