[CPUFREQ] Prepare powernow-k8 for future CPUs.

Forthcoming AMD products will use a different algorithm for transitioning
pstates than the current generation Opteron products do.  The attached
patch allows the powernow-k8 driver to work with those products.

Signed-off-by: Mark Langsdorf <mark.langsdorf@amd.com>
Signed-off-by: Dave Jones <davej@redhat.com>