CPUFREQ: powernow-k8: Try to detect old BIOS, not supporting CPU freq on a recent AMD CPUs.

Make use of FW_BUG interface to give vendors and users the ability to
automatically check for powernow-k8 related BIOS bugs by:
dmesg |grep "Firmware Bug"

Signed-off-by: Thomas Renninger <trenn@suse.de>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>