msm: mdss: fix under-runs for simulator panels

While using simulator panels through debugfs, all the necessary
parameters are updated except panel_max_vtotal. This parameter is used
to derive bandwidth and mdp clock rate for video mode panels. So if this
parameter is not updated while switching simulator panel from low to high
resolution then we are under voting and under clocking MDP. This leads to
under-runs. Fix this by updating panel_max_vtotal with latest v_total.

Change-Id: Ia51340c597e8234d59660b43f19a841ffb96dad3
Signed-off-by: Ujwal Patel <ujwalp@codeaurora.org>