ARM: dts: msm: enable display dimming function for r61318 panel

Enable display backlight dimming function which is a feature from
DDIC to avoid backlight flicker issue when adjust brightness value.

Change-Id: I72ace029f46a0296f4df4d4e78283d258f1620f9
Signed-off-by: Shuo Yan <shuoy@codeaurora.org>