Variable GPU OC: sysfs interface to cycle through different top gpu speeds

- /sys/devices/system/cpu/cpu0/cpufreq/gpu_oc
- for now: 0 = 307mhz, 1 = 384mhz, 2 = 512mhz
- changes take effect immediately of course.

Change-Id: I79f927faf3097b73616fd6bad0d633635903c6b3
Merge "Variable GPU OC: sysfs interface to cycle through different top gpu speeds" into cm-10.1