Change Startek panel to RGB666 mode

-Integrate changes from Mediatek team to change from RGB888 to RGB666
-Change pixel clock, HFP, HBP, VBP
-Modify porch control registers to match changes in panel struct. Note:
HBP and VBP registers are defined as struct H\V_SYNC + H\V_BP

Change-Id: I09bbb519efe541de72b9e779d34d7053ba5c771e