Add auto fullscreen resolution option. Not tested on Linux, let me know if it doesn't work (it probably does).

Fixes issue 6082.

Source/Core/DolphinWX/Src/VideoConfigDiag.cpp

@@ -131,6 +131,7 @@ wxString shader_errors_desc = wxTRANSLATE("Usually if shader compilation fails,
 wxArrayString GetListOfResolutions()
 {
 	wxArrayString retlist;
+	retlist.Add("Auto");
 #ifdef _WIN32
 	DWORD iModeNum = 0;
 	DEVMODE dmi;