[AMDGPU] Don't mark the .note section as ALLOC

Marking a section as ALLOC tells the ELF loader to load the section into memory.
As we do not want to load the notes into VRAM, the flag should not be there.

On AMDHSA, .note is still marked as ALLOC, apparently this is currently
needed for OpenCL (see https://reviews.llvm.org/D74995).

Differential Revision: https://reviews.llvm.org/D76278