MIPS: [turbofan] Use RINT instruction for Float64|32Round ops. on r6.

src/mips64/constants-mips64.h

Index: src/mips64/constants-mips64.h
diff --git a/src/mips64/constants-mips64.h b/src/mips64/constants-mips64.h
index 668c784ed0192894ba91fe52f5a81380f084fc82..4ea5d20b80022c4d3f6da5061ca89b1e640d55ba 100644
--- a/src/mips64/constants-mips64.h
+++ b/src/mips64/constants-mips64.h
@@ -813,7 +813,12 @@ enum FPURoundingMode {
   kRoundToNearest = RN,
   kRoundToZero = RZ,
   kRoundToPlusInf = RP,
-  kRoundToMinusInf = RM
+  kRoundToMinusInf = RM,
+
+  mode_round = RN,
+  mode_ceil = RP,
+  mode_floor = RM,
+  mode_trunc = RZ
 };
 
 const uint32_t kFPURoundingModeMask = 3 << 0;