lpm-levels: Remove hotplug serialization before cluster initialization

In the event where cpu hotplug happens before lpm probe completion,
it fails as the per_cpu cluster variables and the remote spin lock
has not been initialized yet.

There is no need to serialize hotplug before reading all the cluster
levels for the target in the probe. Return the default flag and do
not acquire the remote spin lock in lpm_cpu_pre_pc_cb call.

Change-Id: Idbffa9c3a5ca5b4e8edf280760f26558230eb461
Signed-off-by: Archana Sathyakumar <asathyak@codeaurora.org>