[LoongArch] Updates for the LoongArch ELF psABI v2.01 revision

The e_flags of existing object files are all 0x3 which happens to be
compatible. From this commit on, all LoongArch objects produced with
upstream LLVM will be of object file ABI v1, which is already supported
by binutils' master branch (to be released as 2.40), and is allowed by
the same binutils version to interlink with v0 objects so the existing
distributions have time to migrate.

Differential Revision: https://reviews.llvm.org/D134601