msm: mdss: Use panel supported fps if video is not full screen

In Multiwondow usecase, mdp clk is not scaling to max due to low
video fps. This is causing overall low fps while scrolling in
other window. To accommodate this usecase, use panel supported
fps instead when video is not full screen. This improves overall fps.

Change-Id: I8a1db7e61171f54c15ad3418845fb25c66e4336d
Signed-off-by: Baldev Sahu <bsahu@codeaurora.org>