drivers: thermal: cpu_isolate: core isolate outside critical section

Core isolation and unisolation is done inside the critical section with
the core isolation mutex. There is a possibility of deadlock, when the
core unisolation and core online from userspace happens simultaneously.
To avoid this move the core isolation and unisolation outside the
critical section so that deadlock is avoided.

Change-Id: Ic685a69ce8aa9929a3f12a7d0f287444748f1e26
Signed-off-by: Ram Chandrasekar <rkumbako@codeaurora.org>