ARM: dts: msm: enable DSI timing register double buffering for 8992

Enable double buffer mechanism of dsi timing parameters
so that timing changes can be pick up at next update to
avoid flicking.

Change-Id: I2310dd58c78204e368d3a659db6e813369dd43bb
Signed-off-by: Jeykumar Sankaran <jsanka@codeaurora.org>