[CPUFREQ] Longhaul - Separate frequency and voltage transition

This change should make Longhaul more compatible with
both ver. 2 and Powersaver processors. Voltage transitions
will be done before or after frequency transition. That depends
on direction of change. I don't know how to force conservative
governor when voltage scaling is enabled, so there is only
a warning for user. Minimal voltage is calculated in different
way now because in this way more power is saved at lower
multipliers.

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