[LoongArch] Add a pass to rewrite rd to r0 for non-computational instrs whose...

[LoongArch] Add a pass to rewrite rd to r0 for non-computational instrs whose return values are unused (#94590)

This patch adds a peephole pass `LoongArchDeadRegisterDefinitions`. It
rewrites `rd` to `r0` when `rd` is marked as dead. It may improve the
register allocation and reduce pipeline hazards on CPUs without register
renaming and OOO.