Fifo: rewrite sync on idle skipping hack

Now it's done without a busy loop

Source/Core/VideoCommon/VideoBackendBase.h

@@ -99,7 +99,7 @@ public:
 
 	virtual void Video_GatherPipeBursted() = 0;
 
-	virtual bool Video_IsPossibleWaitingSetDrawDone() = 0;
+	virtual void Video_Sync() = 0;
 
 	// Registers MMIO handlers for the CommandProcessor registers.
 	virtual void RegisterCPMMIO(MMIO::Mapping* mmio, u32 base) = 0;
@@ -148,7 +148,7 @@ class VideoBackendHardware : public VideoBackend
 
 	void Video_GatherPipeBursted() override;
 
-	bool Video_IsPossibleWaitingSetDrawDone() override;
+	void Video_Sync() override;
 
 	void RegisterCPMMIO(MMIO::Mapping* mmio, u32 base) override;