Fifo: Fix SyncGPU.

CBoot::BootUp() did call CoreTiming::Advance which itself blocks on the GPU,
but the GPU thread wasn't started already. This commit moves the SyncGPU
initialization into the Fifo.cpp file and call it after BootUp().

Source/Core/Core/Core.cpp

@@ -498,6 +498,9 @@ void EmuThread()
 
 	CBoot::BootUp();
 
+	// This adds the SyncGPU handler to CoreTiming, so now CoreTiming::Advance might block.
+	Fifo::Prepare();
+
 	// Thread is no longer acting as CPU Thread
 	UndeclareAsCPUThread();