[NFC][RISCV] Simplify the dynamic linker construction logic
The format of dynamic linker is `ld-linux-{arch}-{abi}.so.1`, so
we can just get the arch name from arch type.
Reviewers: asb, kito-cheng, MaskRay
Reviewed By: MaskRay
Pull Request: https://github.com/llvm/llvm-project/pull/97383