[llvm] [RISCV][VLOPT] Add getOperandInfo for saturating signed multiply (PR #120351)

[Michael Maitland via llvm-commits]

michaelmaitland wrote:

I've reverted this patch back to the LGTM, since we decided in #120358 that we will not be adding saturated instructions to isSupportedInstr because of VXSAT.

https://github.com/llvm/llvm-project/pull/120351