[LoongArch] Implement more of the ABI

According to the description of the LoongArch abi documentation,
(https://loongson.github.io/LoongArch-Documentation/LoongArch-ELF-ABI-EN.html)
the calling convention of LoongArch is almost the same as the RISCV's
(except for the vector part), so we borrow the implementation of RISCV.

This patch only guarantees the correctness of lp64d, because only the
part of lp64d is described in detail in the documentation.

Differential Revision: https://reviews.llvm.org/D130249