Adds mdp transfer time to msm dsi binding

Changes in v3:
- Added Rob's R-b
Reviewed-by: NRob Herring <robh@kernel.org>
Signed-off-by: NJeykumar Sankaran <jsanka@codeaurora.org>
Signed-off-by: NRajesh Yadav <ryadav@codeaurora.org>
Signed-off-by: NSean Paul <seanpaul@chromium.org>
Signed-off-by: NRob Clark <robdclark@gmail.com>