disp: msm: dsi: update MDP/DSI transfer time calculation

This change ensure that in cases panel transfer time is specified,
the final transfer time is calculated in accordance with the minimum
threshold time allowed.

Change-Id: I3442d4d3e8a27ec30d93725cb96b229bb94f2ce2
Signed-off-by: Satya Rama Aditya Pinapala <psraditya30@codeaurora.org>