coresight: remove cpu hotplug locking for smp_calls

smp_calls are cpu hotplug safe and so cpu hotplug locking isn't
required to safeguard them. Remove get_online_cpus() and
put_online_cpus() cpu hotplug locking calls that are currently
safeguarding smp_calls against cpu hoplugging.

Change-Id: I527403f4ffe088f3ee65b0b0899b398e1449ab48
Signed-off-by: Pratik Patel <pratikp@codeaurora.org>