make FPSCR.RN an enum

Source/Core/Core/PowerPC/Gekko.h

@@ -7,6 +7,7 @@
 
 #include "Common/BitField.h"
 #include "Common/CommonTypes.h"
+#include "Common/FPURoundMode.h"
 
 // --- Gekko Instruction ---
 
@@ -435,7 +436,7 @@ union UReg_FPSCR
   struct
   {
     // Rounding mode (towards: nearest, zero, +inf, -inf)
-    u32 RN : 2;
+    FPURoundMode::RoundMode RN : 2;
     // Non-IEEE mode enable (aka flush-to-zero)
     u32 NI : 1;
     // Inexact exception enable