mali: add sysfs entries for GPU step 1-5 frequency, voltage, and more

due to an odd issue i was unable to resolve, i'd get bootloops when sysdev_class_create_file()
was called, so i improvised by piggy-backing the sysfs entries in the touchkey driver. yes,
i know, not very classy. :P

- sysfs entries are in /sys/devices/virtual/sec/sec_touchkey/mali_*
- controls for 5 steps of freq/volt/threshold
- control to lock to one step
- control to lock to a range of steps
- control for gpu dvfs sampling rate