Split out gpu/cpu targets based on gpu_library_targets (#20633)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20633
Merge the c2_gpu and is_amd_build logic in targets files.
Reviewed By: dzhulgakov
Differential Revision: D15176621
fbshipit-source-id: 9185b394ffcb305fd8d94dc7c7c92780bf10a511
