[llvm] [RISCV] Make All VType Parts Optional (PR #144971)

[Luke Lau via llvm-commits]

https://github.com/lukel97 commented:

Not blocking for this PR, but do we have tests for when there's gaps between the operands, e.g. `vsetvli x0, x1, e8, ta`? binutils seems to accept this to. Happy if we handle this in a separate PR

https://github.com/llvm/llvm-project/pull/144971