[CPUFREQ] Fix speedstep-smi CPU detection to not run on Pentium 4.

If someone inserts speedstep-smi on a mobile P4, it prevents other cpufreq
modules from loading until it is unloaded.

Signed-off-by: Hiroshi Miura <miura@da-cha.org>
Signed-off-by: Dave Jones <davej@redhat.com>