msm: mdss: synchronize command mode intf stop

In dual DSI command mode case, both interfaces need to finish before the
panel is turned off. In order to make sure these are synchronized, both
interfaces need to be stopped before sending blank/off events to panel
driver.

Change-Id: Ie5bcf5ce53515a5c02696c7be1665c3330be0417
Signed-off-by: Adrian Salido-Moreno <adrianm@codeaurora.org>