Add ClearAll to rasterizer cache for fully wiping the cache on save/load

src/video_core/swrasterizer/swrasterizer.h

@@ -22,6 +22,7 @@ class SWRasterizer : public RasterizerInterface {
     void FlushRegion(PAddr addr, u32 size) override {}
     void InvalidateRegion(PAddr addr, u32 size) override {}
     void FlushAndInvalidateRegion(PAddr addr, u32 size) override {}
+    void ClearAll(bool flush) override {}
 };
 
 } // namespace VideoCore