[AMDGPU] Replace target feature for global fadd32

Change target feature of __builtin_amdgcn_global_atomic_fadd_f32
to atomic-fadd-rtn-insts. Enable atomic-fadd-rtn-insts for gfx90a,
gfx940 and gfx1100 as they all support the return variant of
`global_atomic_add_f32`.

Fixes https://github.com/llvm/llvm-project/issues/61331.

Reviewed By: rampitec

Differential Revision: https://reviews.llvm.org/D146840