[llvm] AMDGPU: Enable RELA for PAL target (PR #128516)

[Jay Foad via llvm-commits]

jayfoad wrote:

I agree that it would be nice to make this change but realistically we can't do it until consumers of PAL ELFs are ready for it. Currently Mesa's ELF loader [is not ready](https://gitlab.freedesktop.org/mesa/mesa/-/issues/10542). There are also parts of the [LLPC](https://github.com/GPUOpen-Drivers/llpc) driver stack that would need updating.

https://github.com/llvm/llvm-project/pull/128516