msm: hotplug: Rectify down_work logic

* Current implementation doesn't seem to work as
  per requirement.
* Our requirement is to get lowest load CPU to take
  it down and at the same time make sure this CPU
  is not locked.
* This patch attempts to implement required logic
  correctly and without looping online CPUs twice.

* This patch is under test, reviews are welcome.

Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>