Tuna : Add display gamma calibration

Allow user to calibrate display gamma.

PS 3: Cleanup code.
      Better gamma values
      Needs: http://review.cyanogenmod.org/48901

PS 4: Restore original commit message

PS 5: Restore old ordering

PS 7: Restore original names of variables & unify both files

Change-Id: I2aa1d746ec6c8372f80e022b786078c5ded68612
tuna: set minimum brightness to 1 instead of 10

Minimum brightness for toroplus (and other tuna-based devices) was
reported as being too bright for night-time usage. It makes sense
logically that the minimum brightness that can be set should be 1
instead of 10, this change is also present in mako.

Change-Id: Id818cdb3a4151e647409f31a3529bf5dbadbed02
JIRA: CYAN-2319
Adapt for API changes.

Adapt for changes made in http://review.cyanogenmod.org/#/c/51499/

Change-Id: I6fc84edd0e4bb6da0b2a9b2be738c44fe16f3929