blc stretch control register
| BLC_R3_STRETCH | this bit configures the stretch feature of bottom right channel. 0: stretch disable, 1: stretch enable |
| BLC_R2_STRETCH | this bit configures the stretch feature of bottom left channel. 0: stretch disable, 1: stretch enable |
| BLC_R1_STRETCH | this bit configures the stretch feature of top right channel. 0: stretch disable, 1: stretch enable |
| BLC_R0_STRETCH | this bit configures the stretch feature of top left channel. 0: stretch disable, 1: stretch enable |