core_ctl: Update cluster nr_run and cpu busy stats under state lock

The cpu busy stats must be updated atomically for all cpus in
a cluster. The nr_run and max_nr stats must be updated atomically
for a cluster. These stats are accessed under state lock else where,
so take the same lock while updating them.

Change-Id: I3ff8eda7982b570105e922209045933cff14b30b
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>
Signed-off-by: Satya Durga Srinivasu Prabhala <satyap@codeaurora.org>