UI: Use dedicated GPU on Hybrid AMD GPU systems

This enables use of the dedicated GPUs for AMD PowerXpress systems.
Especially important for Adapter selection, as usually the dedicated GPU
is hidden/inactive until needed.

Closes jp9000/obs-studio#706

UI/obs-app.cpp

@@ -67,6 +67,11 @@ string opt_starting_collection;
 string opt_starting_profile;
 string opt_starting_scene;
 
+// AMD PowerXpress High Performance Flags
+#ifdef _MSC_VER
+extern "C" __declspec(dllexport) int AmdPowerXpressRequestHighPerformance = 1;
+#endif
+
 QObject *CreateShortcutFilter()
 {
 	return new OBSEventFilter([](QObject *obj, QEvent *event)