cpuset: Make cpusets restore on hotplug

This deliberately changes the behavior of the per-cpuset
cpus file to not be effected by hotplug. When a cpu is offlined,
it will be removed from the cpuset/cpus file. When a cpu is onlined,
if the cpuset originally requested that that cpu was part of the cpuset, that
cpu will be restored to the cpuset. The cpus files still
have to be hierachical, but the ranges no longer have to be out of
the currently online cpus, just the physically present cpus.

Change-Id: I3efbae24a1f6384be1e603fb56f0d3baef61d924

Used commit: https://github.com/7420dev/android_kernel_samsung_zero/commit/4b4bca6c6a37c5ec049ee4a82f858685c1eab8a3