[Object] Support LoongArch in RelocationResolver

Similar to the RISCV logic added in D62062.

With this patch applied, llvm-dwarfdump works on existing LoongArch
object files, but generation of debuginfo on LoongArch is still pending
on proper support for relocations, so no test cases this time. They will
come later.

Differential Revision: https://reviews.llvm.org/D132019