Revert "drm/msm/mdp5: subclass msm_mdss for mdp5"

This reverts commit bc3220be.

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: I3a3f3e9c4066031855159ba6f9b29c3da7e672cc
Signed-off-by: Samantha Tran <samtran@codeaurora.org>