[clang] [lld] [llvm] [RISCV] Make M imply Zmmul (PR #95070)

[Jianjian Guan via cfe-commits]

jacquesguan wrote:

> We intentionally didn't do this because it makes LLVM not work with binutils that doesn't know about Zmmul. Maybe enough time has passed that it is no longer an issue?

Since Zmmul was ratified at june 2022, I think it's OK to update it now. 

https://github.com/llvm/llvm-project/pull/95070