Add basic-level gamma calibration to hardware tunables (1/2)

this depends on Paul Reioux's/ Andrew Dodd's kgamma sysfs
modifications of kernel source code to function

Change-Id: I6d285a7a013d81d2c793d79fa8c1290d43eb7152
Signed-off-by: Daniel Tarrant <daniel.g.tarrant@gmail.com>
merge changes from CyanogenMod 10.2 into local branch