LG Mako gamma control - add mirror interface while leaving
faux's interface in place, respecting his rollover char checksum.

Mirror interface should be a little easier for humans to work
with from scripting (int checksum that doesn't roll over).

Added a couple validation checks to both interfaces before allowing
values to be stored. This will add some safety for scripting or rouge
apps that may have a bug.
-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.

Changed dsi_cmd_desc struct name so it can be shared between
both interfaces.

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