linuxfb: Report WindowManagement capability as false

Just like eglfs does. This will result in dialogs, like file dialogs,
showing up properly centered on the screen.

Change-Id: I2682c7792e4bc66773e31f602a4bee4cf525a6a1
Reviewed-by: Andy Nichols <andy.nichols@digia.com>

src/plugins/platforms/linuxfb/qlinuxfbintegration.cpp

@@ -84,6 +84,7 @@ bool QLinuxFbIntegration::hasCapability(QPlatformIntegration::Capability cap) co
 {
     switch (cap) {
     case ThreadedPixmaps: return true;
+    case WindowManagement: return false;
     default: return QPlatformIntegration::hasCapability(cap);
     }
 }