[llvm-branch-commits] [RISC-V] Use an optional offset for C/Zclsd extension instruction (PR #211674)

[Alexander Richardson via llvm-branch-commits]

https://github.com/arichardson created https://github.com/llvm/llvm-project/pull/211674

Add uimm*_optional via OptionalMemOffsetAsmOperand and use it for the
instructions to allow dropping the "(${rs1})" zero-offset aliases.

This commit was prepared with the help of AI.