sched: add cpu isolation support

This adds cpu isolation APIs to the scheduler to isolate and unisolate
CPUs. Isolating and unisolating a CPU can be used in place of hotplug.
Isolating and unisolating a CPU is faster than hotplug and can thus be
used to optimize the performance and power of multi-core CPUs.

Isolating works by migrating non-pinned IRQs and tasks to other CPUS and
marking the CPU as not available to the scheduler and load balancer.
Pinned tasks and IRQs are still allowed to run but it is expected that
this would be minimal.

Unisolation works by just marking the CPU available for scheduler and
load balancer.

Signed-off-by: Olav Haugan <ohaugan@codeaurora.org>
[rameezmustafa@codeaurora.org: Port to msm-4.9]
Signed-off-by: Syed Rameez Mustafa <rameezmustafa@codeaurora.org>
[markivx: Forward port to 4.14, account for refactor, lack of HMP etc.]
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>

Change-Id: I710fe8e7541357672f4003e78c1839db40a59f1b
[satyap@codeaurora.org: fix compilation issues & indentation issues]
Signed-off-by: Satya Durga Srinivasu Prabhala <satyap@codeaurora.org>