[X86] Remove isCodeGenOnly from (V)ROUND.*_Int and put it on the non _Int form instead.

This matches what's done for VRNDSCALE and most other instructions.

This mainly determines which instruction will be preferred by
disassembler and assembly parser. The printing and encoding
information is the same.

We prefer the _Int form since it uses the VR128 class due to
intrinsic interface. For some of EVEX features like embedded
rounding, we only select from intrinsics today. So there is
only a VR128 version. So making the VR128 version the preferred
is overally consistent.

llvm-svn: 372947