drm/amd/display: Let updates with no scaling changes be fast

[Why]
DC was assuming that any surface_update->scaling_info
meant the update was at least medium.  However, if nothing
has changed there is no scaling to program, so there is
no problem with the update being fast

[How]
If every update flag is not set, the update is fast

Signed-off-by: David Francis <David.Francis@amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Acked-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>