x64Emitter: Prefer MOVAPS to MOVSD

* The high half of regOp is immediately overwritten so the value in it is irrelevant.
* MOVSD produces an unnecessary dependency on the high half of regOp.
* MOVAPS is implemented as a register rename on modern microarchitectures.

Source/Core/Common/x64Emitter.cpp

@@ -2429,8 +2429,14 @@ void XEmitter::MOVDDUP(X64Reg regOp, const OpArg& arg)
   }
   else
   {
-    if (!arg.IsSimpleReg(regOp))
+    if (!arg.IsSimpleReg())
+    {
       MOVSD(regOp, arg);
+    }
+    else if (regOp != arg.GetSimpleReg())
+    {
+      MOVAPD(regOp, arg);
+    }
     UNPCKLPD(regOp, R(regOp));
   }
 }