[CPUFREQ] Longhaul - Option to disable ACPI C3 support

On some motherboards ACPI C3 is available, but it isn't
causing frequency transition on VIA Nehemiah. Longhaul
wasn't working at all earlier, but due to
scaling_cur_speed returning true CPU frequency now, it
looks like CPU is getting stuck at highest frequency
since 2.6.21. I didn't find a reason. Halt is causing
frequency transition.

Signed-off-by: Rafal Bilski <rafalbilski@interia.pl>
Signed-off-by: Dave Jones <davej@redhat.com>