drm/msm/mdp5: don't use autosuspend

It's only likely to paper over bugs.  Unlike the gpu, where we want to
keep things alive a bit longer in expectation of the next frame's
submit, when the display is shut down we can power off immediately.

Signed-off-by: Rob Clark <robdclark@gmail.com>
Acked-by: Archit Taneja <architt@codeaurora.org>