msm: mdss: optimize bw vote for above 720p video playback

On 8909 video decoder supports video decoding up to 30fps.
Optimize the mdp bandwidth voting for video playback by
considering this for resolution greater than 720p.

Change-Id: Ieeaed4e00ad6279cff2e3b5bf1e6a9981581c2ed
Signed-off-by: Shivaraj Shetty <shivaraj@codeaurora.org>