[LoongArch] Optimize the atomic store with amswap_db.[w/d]

When AtomicOrdering is release or stronger, use
    amswap_db.[w/d] $zero, $a1, $a0
instead of
    dbar 0
    st.[w/d] $a0, $a1, 0

Thanks to @xry111 for the suggestion: https://reviews.llvm.org/D128901#3626635

Differential Revision: https://reviews.llvm.org/D129838