S390 [simd]: Unify simd Int to Float rounding

Convert Low I32x4 (S/U) to FP is changed to use
`Round to nearest with ties to even` which is used by ConvertI32x4
as well as the scalar variant ConvertIntToFloat.

Change-Id: Idcb235bdf7fcd43304af785713a4988986db3544
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3032262Reviewed-by: Junliang Yan <junyan@redhat.com>
Commit-Queue: Milad Fa <mfarazma@redhat.com>
Cr-Commit-Position: refs/heads/master@{#75762}

src/compiler/backend/s390/code-generator-s390.cc

@@ -3853,14 +3853,14 @@ CodeGenerator::CodeGenResult CodeGenerator::AssembleArchInstruction(
     case kS390_F64x2ConvertLowI32x4S: {
       __ vupl(kScratchDoubleReg, i.InputSimd128Register(0), Condition(0),
               Condition(0), Condition(2));
-      __ vcdg(i.OutputSimd128Register(), kScratchDoubleReg, Condition(5),
+      __ vcdg(i.OutputSimd128Register(), kScratchDoubleReg, Condition(4),
               Condition(0), Condition(3));
       break;
     }
     case kS390_F64x2ConvertLowI32x4U: {
       __ vupll(kScratchDoubleReg, i.InputSimd128Register(0), Condition(0),
                Condition(0), Condition(2));
-      __ vcdlg(i.OutputSimd128Register(), kScratchDoubleReg, Condition(5),
+      __ vcdlg(i.OutputSimd128Register(), kScratchDoubleReg, Condition(4),
                Condition(0), Condition(3));
       break;
     }