GPU: Flush commands on every dma pusher step.

This commit ensures that the host gpu is constantly fed with commands to
work with, while the guest gpu keeps producing the rest of the commands.
This reduces syncing time between host and guest gpu.

src/video_core/dma_pusher.cpp

@@ -31,6 +31,7 @@ void DmaPusher::DispatchCalls() {
             break;
         }
     }
+    gpu.FlushCommands();
 }
 
 bool DmaPusher::Step() {