[WHY]
Skipping vblank during global sync update request can result in
underflow on certain displays.

[HOW]
Roll back to the previous behavior where DC waits for vblank during pipe
programming.

Fixes: 5d3e1442 ("drm/amd/display: do not wait for vblank during pipe programming")
Tested-by: Mark Broadworth <mark.broadworth@amd.com>
Reviewed-by: Martin Leung <Martin.Leung@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Haiyi Zhou <Haiyi.Zhou@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>