Implement some GPU features (#209)

* Implement stencil testing

* Implement depth testing

* Implement face culling

* Implement front face

* Comparison functions now take OGL enums too

* Fix front facing when flipping was used

* Add depth and stencil clear values

Ryujinx.Graphics/Gal/GalCullFace.cs

@@ -0,0 +1,9 @@
+namespace Ryujinx.Graphics.Gal
+{
+    public enum GalCullFace
+    {
+        Front        = 0x404,
+        Back         = 0x405,
+        FrontAndBack = 0x408
+    }
+}