Jit64: addx - Emit MOV when possible

When the source registers are a simple register and a constant zero and
overflow isn't needed, emitting LEA is kinda silly.

This will occasionally save a single byte for certain registers due to
how x86 encoding works. More importantly, LEA takes up execution
resources while MOV does not.

Before:
41 8D 7D 00          lea         edi,[r13]

After:
41 8B FD             mov         edi,r13d

Source/Core/Core/PowerPC/Jit64/Jit_Integer.cpp

@@ -1346,8 +1346,16 @@ void Jit64::addx(UGeckoInstruction inst)
     {
       RCOpArg& Rimm = Ra.IsImm() ? Ra : Rb;
       RCOpArg& Rreg = Ra.IsImm() ? Rb : Ra;
+
+      if (Rimm.IsZero())
+      {
+        MOV(32, Rd, Rreg);
+      }
+      else
+      {
         LEA(32, Rd, MDisp(Rreg.GetSimpleReg(), Rimm.SImm32()));
       }
+    }
     else
     {
       MOV(32, Rd, Ra);