Small OpenGL Renderer refactoring (#177)

* Call OpenGL functions directly, remove the pfifo thread, some refactoring

* Fix PerformanceStatistics calculating the wrong host fps, remove wait event on PFIFO as this wasn't exactly was causing the freezes (may replace with an exception later)

* Organized the Gpu folder a bit more, renamed a few things, address PR feedback

* Make PerformanceStatistics thread safe

* Remove unused constant

* Use unlimited update rate for better pref

Ryujinx.HLE/Gpu/Engines/INvGpuEngine.cs

@@ -0,0 +1,11 @@
+using Ryujinx.HLE.Gpu.Memory;
+
+namespace Ryujinx.HLE.Gpu.Engines
+{
+    interface INvGpuEngine
+    {
+        int[] Registers { get; }
+
+        void CallMethod(NvGpuVmm Vmm, NvGpuPBEntry PBEntry);
+    }
+}