PowerPC: Make the PowerPCState's msr member variable a UReg_MSR instance

Gets rid of the need to construct UReg_MSR values around the the actual
member in order to query information from it (without using shifts and
masks). This makes it more concise in some areas, while helping with
readability in some other places (such as copying the ILE bit to the LE
bit in the exception checking functions).

Source/Core/Core/PowerPC/PowerPC.h

@@ -75,8 +75,8 @@ struct PowerPCState
   // be manipulated bit by bit fairly easily.
   u64 cr_val[8];
 
-  u32 msr;    // machine specific register
-  u32 fpscr;  // floating point flags/status bits
+  UReg_MSR msr;  // machine state register
+  u32 fpscr;     // floating point flags/status bits
 
   // Exception management.
   u32 Exceptions;