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/GalFrontFace.cs

@@ -0,0 +1,8 @@
+namespace Ryujinx.Graphics.Gal
+{
+    public enum GalFrontFace
+    {
+        CW  = 0x900,
+        CCW = 0x901
+    }
+}