coresight: fix the mutex deadlock issue in cpu hotplug notify path

The CPU hotplug notification path is called up by holding the
cpu_add_remove_lock and when the same is held by the
unregister_hotcpu_notifier() in the notifier path results in deadlock.
So,remove the unregister_hotcpu_notifier() from the notification path as
also the presence of qdss etm notifier doesn't cause any overhead.

Change-Id: I97f150fa053e4e5f58c8cad7cdf2d8ae97a3f774
Signed-off-by: Charan Teja Reddy <charante@codeaurora.org>