This platform is currently relying on the MCPM infrastructure for no
apparent reason.  The MCPM concurrency handling brings no benefits here
as there is no asynchronous CPU wake-ups to be concerned about (this is
used for CPU hotplug and secondary boot only, not for CPU idle).

This platform is also different from the other MCPM users because a given
CPU can't shut itself down completely without the assistance of another
CPU. This is at odds with the on-going MCPM backend refactoring.

To simplify things, this is converted to hook directly into the
smp_operations callbacks, bypassing the MCPM infrastructure.
Tested-by: Wei Xu <xuwei5@hisilicon.com>
Cc: Haojian Zhuang <haojian.zhuang@linaro.org>
Signed-off-by: Nicolas Pitre <nico@linaro.org>