[HIP] Do not use llvm-link/opt/llc for -fgpu-rdc

This patch is a follow up on https://reviews.llvm.org/D81627.

In addition to default -fno-gpu-rdc case, this patches let
HIP toolchain not use llvm-link/opt/llc to link device code
for -fgpu-rdc case. Instead, uses standard lto.

This will eliminate some redundant optimizations and speed
up the compilation/linking.

Differential Revision: https://reviews.llvm.org/D81861