LG Mako generic gamma control - first attempt to create a usable generic
sysfs interface for adjusting gamma without faux123's proprietary app
(while also keeping support for his app).

New checksum routine added that should be easy for humans to work
with (simple int sum instead of a char that rolls over).

Added to sysfs:
/sys/devices/platform/mipi_lgit.1537/kgamma_red
/sys/devices/platform/mipi_lgit.1537/kgamma_green
/sys/devices/platform/mipi_lgit.1537/kgamma_blue

Example:
echo "383 114 21 118 0 0 0 80 48 2" >
/sys/devices/platform/mipi_lgit.1537/kgamma_red

echo "383 114 21 118 0 0 0 80 48 2" >
/sys/devices/platform/mipi_lgit.1537/kgamma_green

echo "383 114 21 118 0 0 0 80 48 2" >
/sys/devices/platform/mipi_lgit.1537/kgamma_blue

First digit is a checksum (sum of all the other 9 numbers)
Gamma Amp 0 = value 6
Gamma Amp 1 = value 7

Show the current settings with proper checksum:
cat /sys/devices/platform/mipi_lgit.1537/kgamma_red
cat /sys/devices/platform/mipi_lgit.1537/kgamma_green
cat /sys/devices/platform/mipi_lgit.1537/kgamma_blue
LG Mako generic gamma control - add a couple checks before trying to
store the values.

-Only allow gamma amp 0 and 1 values up to 31.
-Since we are pushing to a char data type, make sure nothing is over
255.