gamma control register
| GAMMA_UPDATE | Indicates that gamma register configuration is complete |
| GAMMA_B_LAST_CORRECT | this bit configures enable of last b segment correcction. 0: disable, 1: enable |
| GAMMA_G_LAST_CORRECT | this bit configures enable of last g segment correcction. 0: disable, 1: enable |
| GAMMA_R_LAST_CORRECT | this bit configures enable of last r segment correcction. 0: disable, 1: enable |