Simple GPU fixes (#1093)

* Implement RasterizeEnable

* Match viewport count to hardware

* Simplify ScissorTest tracking around Blits

* Disable RasterizerDiscard around Blits and track its state

* Read RasterizeEnable reg as bool and add doc

Ryujinx.Graphics.Gpu/State/GpuState.cs

@@ -117,6 +117,9 @@ namespace Ryujinx.Graphics.Gpu.State
         /// </summary>
         private void InitializeDefaultState()
         {
+            // Enable Rasterizer
+            _backingMemory[(int)MethodOffset.RasterizeEnable] = 1;
+
             // Depth ranges.
             for (int index = 0; index < 8; index++)
             {