drm/amd/display: Optimize front end programming.

for video scaling changes,
Reduce reg access count from 1044 to 447, duration time
from 4.6ms to 3ms.

Signed-off-by: Yongqiang Sun <yongqiang.sun@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>