[llvm] [RISCV] Use GPRNoX0 instead of AVL for Xsfmm pseudos. NFC (PR #170726)

[Craig Topper via llvm-commits]

topperc wrote:

> LGTM. Did this ever cause problems in RISCVInsertVSETVLI?

We don't use the `selectVLOp` `ComplexPattern` for these instructions in SelectionDAG so there was no way to create the operand with an immediate. I think if we did it would probably crash or do something wrong in RISCVInsertVSETVLI.

https://github.com/llvm/llvm-project/pull/170726