Revert "drm/msm/disp/dpu: Remove unused code from drm_crtc.c"

This reverts commit c17aeda0.

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 the 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: I95d0c65a978866354996d3160bb06bca4387f598
Signed-off-by: Samantha Tran <samtran@codeaurora.org>