[CPUFREQ] e_powersaver: Check BIOS limit for CPU frequency

Call ACPI function to get BIOS limit for CPU frequency.
Fail if processor would like to run at higher frequency.
Allow user to ignore BIOS limit.

eps: Detected VIA Model D C7-M
eps: Current voltage = 1084mV
eps: Current multiplier = 16
eps: Highest voltage = 1084mV
eps: Highest multiplier = 16
eps: Lowest voltage = 844mV
eps: Lowest multiplier = 4
eps: ACPI limit 1.60GHz

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