msm: mdss: add mdp clock calculations for BWC decode

BWC decode works at 2 pixels/clk and MDP clock requirement needs to be
adjusted to account for this. If BWC decode is enabled and MDP clock is
not sufficient then real-time pipeline might suffer from throughput
delays and might result in under-runs. Prevent this by calculating MDP
clock rate when BWC decode is needed and then choose max MDP clock rate
by comparing normal MDP clock and bwc MDP clock.

Change-Id: I92afc5a3c7ec29602ffdeec1ada0d67c57c4497f
Signed-off-by: Ujwal Patel <ujwalp@codeaurora.org>