drm/amd/display: SubVP missing scaling case

[Description]
For SubVP scaling case we have to combine
the plane scaling and stream scaling.

Use UCLK dummy p-state WM for FCLK WM set C

[Description]
For DCN32/321 program dummy UCLK P-state watermark into FCLK
watermark set C register.

Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Reviewed-by: Nevenko Stupar <Nevenko.Stupar@amd.com>
Acked-by: Brian Chang <Brian.Chang@amd.com>
Signed-off-by: Alvin Lee <Alvin.Lee2@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>