CPU hotplug support doesn't have to be set up until fairly late in the
boot process, so it can be done in a regular initcall. To make sure that
we don't miss any ordering problems in the future, output a warning if
any of the functions are called before initialization has completed.

This is part of untangling the boot order dependencies on Tegra so that
more code can be shared between 32-bit and 64-bit ARM.
Signed-off-by: Thierry Reding <treding@nvidia.com>