Some DSI panels require changing backlight intensity through DSI
command. Create a backlight driver hook to Tegra DSI to achieve
these panels.

Bug 1453606

Change-Id: I1c7466c01cde101e8e8346cb27371d35ff48ed58
Signed-off-by: Roger Hsieh <rhsieh@nvidia.com>
Reviewed-on: http://git-master/r/380396


Reviewed-by: Bharat Nihalani <bnihalani@nvidia.com>
Tested-by: Bharat Nihalani <bnihalani@nvidia.com>