Variable GPU OC: sysfs interface to cycle through different top gpu speeds (by imoseyon) and set 384 MHz GPU speed as default.

- sysfs control path: /sys/devices/system/cpu/cpu0/cpufreq/gpu_oc
  0 = 307mhz, 1 = 384mhz, 2 = 512mhz

Source: https://github.com/edoko/AirKernel_GN_JB/commit/8f8698154d5424853e814f1b4cb8542a63780c6f

Note boype: Finally got it working properly after examining the code; also slightly adjusted GPU voltages so that the 512 MHz OPP gets a little more current than the 384 MHz OPP.