drm/msm/sde: update dp timings to make it bottom-right

This change updates the porches as per the hardware programming
guide recommendation to make the dp timings bottom right. Along with
this it disables the prefetch since shifting the timing there is
no need to prefetch the pixels.

Change-Id: I60e29b2e7f16b16a06c8c7702012e0e74c946ff6
Signed-off-by: Abhijit Kulkarni <kabhijit@codeaurora.org>