Memory: Remove count of cached pages and add InvalidateRegion

In a future commit, the count of cached pages will be reintroduced in
the actual surface cache. Also adds an Invalidate only to the cache
which marks a region as invalid in order to try to avoid a costly flush
from 3ds memory

src/video_core/swrasterizer/swrasterizer.h

@@ -11,7 +11,7 @@ namespace Pica {
 namespace Shader {
 struct OutputVertex;
 }
-}
+} // namespace Pica
 
 namespace VideoCore {
 
@@ -22,6 +22,7 @@ class SWRasterizer : public RasterizerInterface {
     void NotifyPicaRegisterChanged(u32 id) override {}
     void FlushAll() override {}
     void FlushRegion(PAddr addr, u32 size) override {}
+    void InvalidateRegion(PAddr addr, u32 size) override {}
     void FlushAndInvalidateRegion(PAddr addr, u32 size) override {}
 };