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
Signed-off-by: Grarak <williye97@gmail.com>

Conflicts:
	arch/arm/mach-omap2/omap2plus-cpufreq.c