core_ctl: Increase MAX_CPUS_PER_CLUSTER to 6

It is possible to have more than 4 CPUs in a cluster. Increase
the MAX_CPUS_PER_CLUSTER to 6.

Change-Id: I6b16a6a079f97c3101e409c5e569a2906f1571ba
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>
Signed-off-by: Satya Durga Srinivasu Prabhala <satyap@codeaurora.org>