powernow-k8: Let cpufreq driver handle affected CPUs

Let the cpufreq driver manage AMD Dual-Core CPUs being tied together.

Since cpufreq driver's affected CPUs data, cpufreq_policy->cpus, already
knows about which cores are tied together, powernow driver does not have
keep its internal data for every core.  (even a pointer.. it will never
be called on)  Telling cpufreq driver about cpu_core_map at init time is
sufficient.
Signed-off-by: Jacob Shin <jacob.shin@amd.com>
Signed-off-by: Dave Jones <davej@redhat.com>