voltage control: sysfs interface

Merge following commits from faux123
* 1325f21 - Voltage Control: add sysfs interface (4 months ago)
* d33d71d - Voltage Control: initial voltage control for MSM S4-Pro SOC (4 months ago)

- Allows for voltage control by android apps
- Added additional tables for overclocking inside acpuclock-8064.c (not enabled yet in build config)