Revert "arch: arm: omap4: bump 307MHz GPU to 384MHz without increasing the voltages and add an extra OPP with 512MHz to compensate for the weak GPU and low memory bandwidth, which is, in this device's case, its major bottleneck."

This reverts commit 0e0e1842222a58cea3ac8e987b3e240d2d91df42.
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