If you choose default output to DVI, the LCD backlight used to
stay on, since panel->disable function never gets called.

So, during init put backlight GPIO to off state and the driver
code will decide which output to enable.
Signed-off-by: Vaibhav Hiremath <hvaibhav@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>