Revert "drm/msm: Move wait vblanks to mdp complete_commit hook"

This reverts commit a5c6b599.

This reversion is happening as a result of disabling the
disp/dpu directory as it will not be used in 4.19 downstream
display driver and these changes are made in a common layer
which affects the downstream driver functionalities. Separate
patches are submitted to revert the upstream driver and
introduce the downstream version of the display driver.

Change-Id: Iddf8656b38631ceb20fec34e0fb6cc753db81ed2
Signed-off-by: Samantha Tran <samtran@codeaurora.org>