Revert "gl: Use GstGLDisplayEGL directly instead of creating a GstGLDisplayVIVFb subclass"

This reverts commit 47fd4d391e775c11f529705bb0f457a9d25ba5e7.

This patch is incorrect. It doesn't actually compile, and causes a crash
because the viv-fb window implementation needs a native EGL handle
to pass to fbCreateWindow, but the GstGLDisplayEGL handleis actually
an EGLDisplay now (and gets cast to the wrong type)

ext/qt/gstqtglutility.cc

@@ -169,7 +169,11 @@ gst_qt_get_gl_wrapcontext (GstGLDisplay * display,
   }
 #endif
 #if GST_GL_HAVE_PLATFORM_EGL && defined (HAVE_QT_EGLFS)
+#if GST_GL_HAVE_WINDOW_VIV_FB
+  if (GST_IS_GL_DISPLAY_VIV_FB (display)) {
+#else
   if (GST_IS_GL_DISPLAY_EGL (display)) {
+#endif
     platform = GST_GL_PLATFORM_EGL;
   }
 #endif