Revert "percpu: add __percpu to SHIFT_PERCPU_PTR"

This reverts commit 825dbc6f.

I mistakenly applied this and only now have thought about it a little
more and had time to evaluate a kbuild error for dmaengine.

Once we're calling RELOC_HIDE, we're moving back into the __kernel
address space and letting users interact with the actual memory address
rather than in __percpu which is before adding the offsets.

Signed-off-by: Dennis Zhou <dennis@kernel.org>