drivers: thermal: cpu-cooling: unisolate CPU after hotplug

If a CPU that has been isolated is offlined, as per the
recommendation the CPU has to be unisolated. The existing CPU cooling
device doesn't handle this scenario.

Register for CPU hotplug state callback and unisolate the CPU after it
is hotplugged. When the CPU is brought back online, veto it from
coming online and bring it back online later when the isolation request
is cleared.

Change-Id: I1d73f3a0610b73b67e94900ec38d59402021289b
Signed-off-by: Ram Chandrasekar <rkumbako@codeaurora.org>