RasterizerCache Redesign: Flush

flushing is now responsability of children caches instead of the cache 
object. This change will allow the specific cache to pass extra 
parameters on flushing and will allow more flexibility.

src/video_core/renderer_vulkan/vk_buffer_cache.h

@@ -49,8 +49,6 @@ public:
         return alignment;
     }
 
-    // We do not have to flush this cache as things in it are never modified by us.
-    void Flush() override {}
 
 private:
     VAddr cpu_addr{};
@@ -87,6 +85,10 @@ public:
         return buffer_handle;
     }
 
+protected:
+    // We do not have to flush this cache as things in it are never modified by us.
+    void FlushObjectInner(const std::shared_ptr<CachedBufferEntry>& object) override {}
+
 private:
     void AlignBuffer(std::size_t alignment);