[lld] [lld][LoongArch] Partially fix the handling of R_LARCH_PCALA64_* relocs (PR #73387)

[Xi Ruoyao via llvm-commits]

xry111 wrote:

IMO we should document the "recommended practice" for R_LARCH_PCALA64_* and use the same algorithm everywhere.

https://github.com/llvm/llvm-project/pull/73387