Implement vertex instancing (#381)

Ryujinx.Graphics/Gal/GalPipelineState.cs

@@ -7,6 +7,8 @@
         public bool Enabled;
         public int Stride;
         public long VboKey;
+        public bool Instanced;
+        public int Divisor;
         public GalVertexAttrib[] Attribs;
     }
 
@@ -22,6 +24,8 @@
         public float FlipX;
         public float FlipY;
 
+        public int Instance;
+
         public GalFrontFace FrontFace;
 
         public bool CullFaceEnabled;