pstate: set all cores to nominal freq/volt during boot.

As last step of boot process determine the nominal pstate for each
core and set it as the current operating value.

Change-Id: Ifc452977d89971e84f73177885306aa3259408f4
Reviewed-on: http://gfw160.aus.stglabs.ibm.com:8080/gerrit/13350
Tested-by: Jenkins Server
Reviewed-by: Daniel M. Crowell <dcrowell@us.ibm.com>
Reviewed-by: A. Patrick Williams III <iawillia@us.ibm.com>