drm/amd/display: wait for updates to latch before locking

[why&how]
It is possible for an update to acquire otg lock and begin programming
while the previous update has not completed and its values have not
latched. The correct way to go about this is to wait until the vupdate
pulses so we can be sure that previous updates have latched and we can
continue with the current update pipe programming, otherwise during
consecutive full updates we will have corruption flash on the screen.

The corruption flash occurs specifically on configs that require odm
combine, and its local to a specific pipe (will not flash across whole
screen). This ticket is across the otg slave, but it may also appear
across master.

Reviewed-by: Leo Chen <leo.chen@amd.com>
Signed-off-by: Ausef Yousof <Ausef.Yousof@amd.com>
Signed-off-by: Roman Li <roman.li@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>