[llvm] [RISCV] Add OperandType for vector rounding mode operands. (PR #114179)

[Philip Reames via llvm-commits]

https://github.com/preames approved this pull request.

LGTM, but it feels a bit weird to have a single operand type for both VXRM and FRM.  Do we have a single instruction/pseudo which dynamically could be either?  If not, why not split the operand type by FRM and VXRM?

https://github.com/llvm/llvm-project/pull/114179