Revert "drm/msm: dpu: 'vsync' replac 'vsync_clk' in cmdmode enc"

This reverts commit 2c1f748d.

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 display driver.

Change-Id: Ibf9420e350b6b58aa48df9feaa4eee3f729cf2fc
Signed-off-by: Samantha Tran <samtran@codeaurora.org>