[llvm] [RISCV] Add a PseudoVSETVLIX0X0 pseudo for the x0, x0 vsetvli. NFC (PR #141875)

[Craig Topper via llvm-commits]

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topperc wrote:

Removed and updated the code to check opcode instead of register for the VLMAX case.

https://github.com/llvm/llvm-project/pull/141875