X86: Implement a media xor microop.

src/arch/x86/isa/microops/mediaop.isa

@@ -334,4 +334,11 @@ let {{
             }
             FpDestReg.uqw = result;
         '''
+
+    class Mxor(MediaOp):
+        def __init__(self, dest, src1, src2):
+            super(Mxor, self).__init__(dest, src1, src2, 1)
+        code = '''
+            FpDestReg.uqw = FpSrcReg1.uqw ^ FpSrcReg2.uqw;
+        '''
 }};