disp: msm: dsi: refine the logic for mode filling and calculation

Video and command mode will be included in same timing node
when POMS is enabled, but DFPS is only applicable for video
mode, so add this change to differentiate panel mode, and fill
display mode according to panel mode.

Change-Id: I6aa0f8572f23f0612684ed7cdf406b20ab3df822
Signed-off-by: Lei Chen <chenlei@codeaurora.org>