drivers: cpufreq: add support for scaling available frequencies

this patch implements sysfs for scaling
between available cpu frequencies

also, it sets a safe limits during boot process

min: 200MHz
max: 1400|1600MHz

This change reverts this patch
https://gerrit.omnirom.org/#/c/5685/

Signed-off-by: Humberto Borba <humberos@gmail.com>
Change-Id: Ia424ee5fd125a9d45839091d8bd7057b8e560c15