drm/msm/mdp5: Add missing mdp5_enable/disable calls

Since runtime PM isn't implemented yet, we need to call
mdp5_enable/disable in a few more places. These would later be
replaced by runtime PM get/put calls.

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