arch-mips: add regWidth constant to float regfile

src/arch/mips/regfile/float_regfile.hh

@@ -85,6 +85,7 @@ namespace MipsISA
         FloatReg32 regs[NumFloatRegs];
 
       public:
+        static const int regWidth = SingleWidth;
 
         void clear();
         double readReg(int floatReg, int width, unsigned tid = 0);