percpu: disallow archs from overriding SHIFT_PERCPU_PTR()
It has been about half a decade since all archs started using the
dynamic percpu allocator and thus the same SHIFT_PERCPU_PTR()
implementation. There's no benefit in overriding SHIFT_PERCPU_PTR()
anymore.
Remove #ifndef around it to clarify that this is identical regardless
of the arch.
This patch doesn't cause any functional difference.
Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Christoph Lameter <cl@linux.com>