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.GAL/IPipeline.cs

@@ -48,6 +48,8 @@ namespace Ryujinx.Graphics.GAL
 
         void SetProgram(IProgram program);
 
+        void SetRasterizerDiscard(bool discard);
+
         void SetRenderTargetColorMasks(uint[] componentMask);
 
         void SetRenderTargets(ITexture[] colors, ITexture depthStencil);