drm/amd/display: refactor dc_update_surfaces_for_stream

- reuse existing helper functions
- helper function to make it more obvious which cases we can do optimize programming
Signed-off-by: Tony Cheng <tony.cheng@amd.com>
Reviewed-by: Yongqiang Sun <yongqiang.sun@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>