VideoCore: Unify interface to OpenGL and SW rasterizers

This removes explicit checks sprinkled all over the codebase to instead
just have the SW rasterizer expose an implementation with no-ops for
most operations.

src/video_core/swrasterizer.h

@@ -0,0 +1,26 @@
+// Copyright 2015 Citra Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include "common/common_types.h"
+
+#include "video_core/rasterizer_interface.h"
+
+namespace VideoCore {
+
+class SWRasterizer : public RasterizerInterface {
+    void InitObjects() override {}
+    void Reset() override {}
+    void AddTriangle(const Pica::Shader::OutputVertex& v0,
+            const Pica::Shader::OutputVertex& v1,
+            const Pica::Shader::OutputVertex& v2);
+    void DrawTriangles() override {}
+    void FlushFramebuffer() override {}
+    void NotifyPicaRegisterChanged(u32 id) override {}
+    void FlushRegion(PAddr addr, u32 size) override {}
+    void InvalidateRegion(PAddr addr, u32 size) override {}
+};
+
+}