drm/amd/display: Only update mpc blend config if not full update

The current mpcc insert/remove logic does not support updating
only a single mpcc. So when pixel alpha changed but no full update
we can mistakenly shuffle the mpcc layering order. With this change
we will only insert/remove mpcc if there is full update.

Signed-off-by: Eric Yang <Eric.Yang2@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>