[LoongArch][NFC] Fix the operand constraint of AMCAS instructions (#114508)

The `rd` operand of AMCAS instructions is both read and written, because
of the nature of compare-and-swap operations, but currently it is not
declared as such. Fix it for upcoming codegen enablement changes. In
order to do that, a piece of LoongArchAsmParser logic that relied on
TableGen-erated enum variants being ordered in a specific way needs
updating; this will be addressed in a following refactor. No functional
change intended.

While at it, restore vertical alignment for the definition lines.

Suggested-by: tangaac <tangyan01@loongson.cn>
Link:
https://github.com/llvm/llvm-project/pull/114398#discussion_r1825362676

0 files changed, 0 insertions, 0 deletions