ARM: dts: msm: enable three displays on 8996 auto platforms

Enable the third display on DSI-1 interface through DSI-HDMI
bridge chip for MSM8996 Auto platforms. Two of DSI-HDMI displays
are fixed to 1920x1080 for now.

Change-Id: I42e60c317aab4ee490e27dfe996d419bc879165d
Signed-off-by: Jin Li <jinl@codeaurora.org>