[llvm] [RISCV][AsmParser] Allow parsing vset{i}vli omitting LMUL parameter (PR #115277)

[Craig Topper via llvm-commits]

topperc wrote:

> @topperc I'm sorry to bother you, could you address the last comment, please?

I'm not sure we should support it since the spec no longer indicates it is optional.

As far as I know all fields are optional in binutils so if we're just doing it for compatibility, why only make 1 field optional?

https://github.com/llvm/llvm-project/pull/115277